WASHINGTON — Elizabeth Warren looks to be the primary beneficiary of President Donald Trump's Ukraine scandal and the House impeachment inquiry into it, but Joe Biden's allies think there's an opportunity for him to rally voters — especially if he gets more aggressive in going after Trump.

That friction goes to the heart of Biden's "electability" argument and could make the next several weeks decisive in the race for the Democratic nomination to take on Trump next November.

It could be that Trump's focus on Biden persuades Democrats that the former vice president is the toughest candidate, or it could be that primary voters fear Trump's allegations against Biden would weaken him in a general election, regardless of the truth.

Warren's allies are careful in how they frame the Ukraine narrative as helpful to her — obviously sensitive to Biden's popularity in the party, their own candidate's aversion to attacking competitors and Democrats' anger with Trump for trying to enlist a foreign government's help in dragging a political opponent's name through the mud.

"This latest Trump corruption scandal is unifying Democrats everywhere — including the presidential race — and Elizabeth Warren had staked out a leadership position on this (impeachment) fight, so I think a lot of people are giving her credit," said Adam Green, co-founder of the Progressive Change Campaign Committee, which has endorsed Warren.

And, he added, Warren made "systemic corruption the centerpiece of her campaign since Day One."

But some Democratic insiders say the real reason the Ukraine issue lines up as a boost to Warren — who has climbed into a virtual tie with the former vice president in several recent polls — is that Biden's name is inextricably linked to it.

"The idea that this is going away for Biden because Democrats are going to defend him? It's not going away," said Patti Solis Doyle, who served as Biden's chief of staff when he ran for vice president in 2008. "It's going to be front and center for ... as long as this impeachment goes on. It's (Trump's) only defense.”

Biden has pushed back on Trump's claims that the Ukraine business dealings of the former VP's son were suspect in tones strong enough to suggest Biden understands that there is a threat to his fortunes — and that there's a chance he can turn Trump's attacks on him into a patriotic rallying cry.

"I can take the political attacks," Biden said. "They'll come and they'll go, and in time they'll soon be forgotten, But if we allow a president to get away with shredding the United States Constitution, that will last forever."

There's some sentiment in Biden's camp that the vice president should go harder at Trump than he has so far, one source with knowledge of internal discussions told NBC news.

"(The) VP is more measured," the source said in an electronic message. "We do need to rally the party and the base around this. It's a constitutional crisis, not just an election."

Democratic insiders sympathetic to Biden outside his campaign also praised his response but echoed the advice that he should become more aggressive.

The heart of the Ukraine scandal is the president's effort to get his Ukrainian counterpart to dig up dirt on Biden and his son, Hunter Biden. That push was made at a time when the White House was withholding congressionally appropriated aid to the Eastern European nation and when, as is currently the case, Trump's campaign team saw Biden as the biggest risk to his re-election.

A former Ukrainian prosecutor told The Washington Post on Thursday that an investigation into the gas company for which Hunter Biden served as a board member yielded no evidence that the younger Biden engaged in illegal activity. But the absence of evidence hasn't stopped Trump, his campaign and leading surrogates for him from accusing the Bidens of corruption.

Most Democrats, including Warren fans, believe Biden is being unfairly slimed by Trump, and his rivals have been unified in condemning the president. But there are quiet concerns within the party that 2020 could turn into a replay of 2016, when eventual nominee Hillary Clinton's private email server was put on the back burner during the Democratic primary only to resurface as Trump's top weapon against her in the general election.

One presidential campaign veteran who is neutral in the current race said that's why Biden needs to "lean in" to striking back more aggressively at Trump and stirring up the sympathies of the Democratic base.

The source familiar with Biden campaign discussions said memories of 2016 will make it easier, not harder, for the former vice president to win over Democrats in the primary.

"I think voters now know Trump's game and won't fall for that," the source said. "They'll see Trump as so worried about Biden that he's willing to get impeached to save him from getting beaten like a drum."

The timing of the impeachment process also is important, as Speaker Nancy Pelosi has told her colleagues she wants the inquiry into Trump to be done expeditiously. If they are successful in that, an impeachment vote could occur at least a few weeks before the Iowa caucuses in early February.

For Warren, who has managed to stay out of internecine warfare, there's little apparent risk in a fight between the parties over allegations of corruption.

"If there's one thing Warren does not have, it's shady business deals," Solis Doyle said.