Impeachment outcome is a foregone conclusion, but how Trump's defence tackles Biden could sway voters

• WHAT'S HAPPENING: U.S. President Donald Trump has been impeached and is on trial for abuse of power and obstruction ofCongress in connection with his attemptto get Ukraine to investigate a political opponent.
  
• WHAT'SNEXT: Trump's defence team has resumed arguments Monday at 1 p.m ET.

• WHAT'S NEW:Democratic presidential candidate Joe Biden and his son, Hunter, are likely to come up this week as the defence argues that Trump was justified in wanting to probe their activities in Ukraine.

• WHAT TO WATCH: The debate over whether to allow additionalwitnesses has heated upin wake of revelations from former national security adviser John Bolton that undermine Trump's defence.

Democratic presidential candidate Joe Biden was not central to the defence team's brief opening argumentsin the Senate trial of U.S. President Donald Trump, buthowthe lawyers paintthe former vice-president's role in the Ukraine affair at the heart of the impeachment process when they resume arguments Monday could prove consequential in the November election.

In their two-hour opening argument Saturday, Trump's legal team tried to undercutthecentral assertion of the Democrats' impeachment case: that Trump held up $400 million US inmilitary aid in an attempt to exact Ukraine's help in underminingBiden, whom he saw as his likely rival in the 2020 election.

Given that there is no chance the Republican-majority Senate will vote to remove Trump, using the trial to throwshade at Biden might helplightensome of the baggage Trump will be carrying into the electoral race.

WATCH: Trump's legal team takes aim at Democrats'impeachment case in its opening arguments Saturday:

They used some of the same witness testimony deployedby the House managers prosecuting the caseto suggest that none of the U.S. officials and diplomats testifying had direct knowledge of an explicit quid pro quo between Trump and Ukrainian President Volodymyr Zelensky.

They painted Trump as a reformer concerned aboutcorruption and "burden sharing" ensuring that other European nations do their fair share to support Ukraine.

But it's questions around Biden and his son Hunter's activities in Ukraine, which on their face have little to do with the underlying articles of impeachment being litigated in the Senate, that could have an impact on the true intended audience ofthe Senate trial: American voters.

'The intent is to just muddy the waters'

No one is expecting Trump's legal team to reveal anything newabout Hunter Biden's 2014 appointment to the board of the Ukrainian energy company Burisma and his father's role in the resignation of the prosecutor-general who was meant to be investigating alleged corruption at the firm.

But it doesn't have to in order for the tactic to benefit Trump.

"They're not going to be able to prove that a crime was committed by Hunter Biden but the intent is to just muddy the waters," said Bradley Moss, a national security attorney and partner in the D.C. law firm Mark S. Zaid, which represents the whistleblower who first raised concerns about Trump's dealings with Zelensky although Moss is not involved in that case.

"They don't have to win so much as they just have to throw mud at the scene."

Merely by raising the issuethey will have accomplished, in essence, what Trump was askingZelensky to do on the now infamous July 25, 2019, call: publicly raise questions about Biden's actions in Ukraine, thereby planting seeds of doubt in the minds of voters.

"What came out in the witness testimony is the president didn't care whether there was actually an investigation; he just wanted an announcement of an investigation," said Frank O. Bowman, a professor at the University of Missouri School of Law and a visiting professor at the Georgetown Law Center in D.C.

"This is going to be even better. It's now in front of American televisions and tens of millions of people watching." (Actual viewership so far has been closer to eight million).

WATCH | As anticipated, Trump's defence team spent part of Monday's arguments highlighting the Bidens' connections to Ukraine and Burisma:

'Raised flags almost immediately'

5 years ago

Duration 4:50

Attorney Pam Bondi runs through some of the reactions from media and colleagues to Hunter Biden's appointment to the board of Ukrainian energy company Burisma.

Not all Republicans on board

The Washington Post has reported that not all Republicans are on board with this strategy.

In the corridors of the Senate and on U.S. cable news networks this past week, several Republicans did raise the prospect of the Bidens testifying. There was even talk of a witness swap at one point the Bidens for acting White House chief of staff Mick Mulvaney and former national security adviser John Bolton which Biden and the Democrats shot down.

Sen. Ted Cruz told radio talk show host Hugh Hewitt that he advised the defence team that "nothing matters more than the facts on Burisma" and urged them to "lay out substantive, factual reasons why investigating Burisma, the president had a responsibility to do so."

But others, such as Jim Jordan, a vocal defender of Trump, have urged the defence team to focus on dismantling what he and fellow Republicans see as hearsay evidence;questioning how the Democratswent about conducting the impeachment inquiry; and attacking the character of their star prosecutor, Adam Schiff.

Where Biden is vulnerable

The fact that the Bidens haven't offered much of an explanation in the months since the Burisma case became central in the Trump-Ukraine affair has given air to the innuendo that keeps this issue on the front burner of the Republicans' strategy.

Biden Jr. has said little about how or why he got the appointment beyond having held board positionsat Amtrak and the World Food Program USAbutsaid in an ABC News interview that in hindsight it was badjudgment but not an ethical lapse. He hasn't disclosed how much he was paid for the gig, which he left in April 2019.

Biden Sr., for his part, said he and his son never discussed the role and has bristled when asked about the issue.Last week, his 2020 campaign team released a video debunking some of the Burisma-related claims.

While there seems to belittle doubt that Biden's push to have prosecutor-general Viktor Shokin removed in 2016 was in line with a U.S. foreign policy supported by European allieswith an interest in democratic reform inUkraine, there's also no question that Hunter Biden's appointment raised eyebrows from the minute it became public in 2014.

Not only were there questions about conflict of interest raisedin the U.S. press and in Ukraine at the time, U.S. State Department officials testifiedat the House impeachment hearings last November thatthe diplomatic corps, too, was concerned about the appearance of nepotism.

MEDIA: In the House impeachment hearings in November, some witnesses spoke about the Burisma affair:

Diplomat George Kent questioned on Hunter Biden's business credentials

5 years ago

Duration 1:04

Testifying to Congress, diplomat George Kent faces a barrage of questions about Hunter Biden's suitability to sit on a board of directors in Ukraine

The cavalier way Joe Biden boasted in a 2018 public appearanceabout removing Shokin does himno favours either.

When these and other points come up atthe Senate trial, it'll be hard forthe House managers arguing the case against Trump to challenge them. Unlike in a criminal trial, there is no rebuttal process per se. There will be a short period set aside for argument, but that only comes after the defence has laid out its case and senators have submitted questions.

"[They] are going to be able to throw this innuendo around and not have to prove any of it," said Bowman. "It's the one point at which you might get an interesting fight over questions of relevance."

Why it might backfire

Democrats anticipated a Biden-focused attack and used part oftheir second day of arguments last week to preemptively undermine it. They pointed out that Shokinwas not actively investigating Burisma at the time that he was pushed out, and the investigation he was supposed to do concerned allegations of money laundering and tax evasion byBurisma's owner that predatedHunter Biden's appointment.

Shokin's removal wasn't Biden's initiative alone, they argued, but rather part of a bipartisan push for justice reform in Ukraine supported by several Republican lawmakers at the time.

While Trump's legal team will try to paintconcern over Burismaas part of his intended clampdown on corruption, there is little evidence that Trump had an interest in investigating corruption within Burisma or in Ukraine prior to Biden entering the presidential race in April 2019.

What do voters think

Heading into next week's caucuses in Iowa, Biden remains the Democrats' frontrunnerin national polls, but several recent state polls show Bernie Sanders overtaking him in Iowa and New Hampshire.

If Trump's lawyers push a Biden-focused line of attack this week, that could earn Biden some sympathy with primary voters.

"The Democrats are angry enough about how this has gone down that they will kind of lean towards him, if only out of defence of the party," Moss said.

The general election, however, is another matter.

Support for removing Trump from office has barely budged since the House voted to impeach the president in December, with just under 47 per cent of Americans supporting removal as of Jan. 24, according to the polling site FiveThirtyEight.

Among Republicans, it inched up slightly since the start of the Senate trial, from just under eight per cent to 10 per cent. Democrats' support sits at 84 per cent.

Attention turns to witnesses

The defence team has one more day to present its case before the trial moves to the up to 16-hour question phase, where senators submit questions in writing that will be read out by Chief Justice of the Supreme Court John Roberts, who is presiding over the trial.

Senators will then have a chance tovote on whether to allow additionalwitnesses and documentary evidence.

That question gained new urgency late Sunday when the New York Times reported that former national security adviser John Bolton writes ina forthcoming book that Trump told him last August that he would continue to freezethe $400 million in aid until the Ukrainians followed through on the Biden investigation.

• READ the House managers' response to Bolton revelations

Trump immediately took to Twitter to deny the claim.

Fifty-one senators have to vote in favour for the witness motion to pass, and the Democrats in the Senate number only 47. Sen. Mitt Romney, who is considered to be one of the Republicans who may be swayed to vote with the Democrats, said Monday that while he'll wait for the defence to complete their arguments, it's clear Bolton has relevant testimony to provide.

"It's increasingly likely that other Republicans will join those of us who think we should hear from John Bolton," he told ABC News.