Joe Biden may have inadvertently triggered the scandal now threatening Donald Trump's presidency, but it has also impacted his own White House bid and the Democrat could soon learn whether it dooms his candidacy or bolsters it.

The two septuagenarians are at the center of a Washington maelstrom featuring an impeachment inquiry, intense partisan feuding and repeated attacks on Biden by a president apparently eager to create a fog of confusion over his potential 2020 election rival.

Trump has admitted seeking help from Ukraine's president to investigate Biden on a phone call at the heart of a whistleblower complaint which has prompted House Democratic leadership to launch a formal impeachment probe against Trump.

He has also darkly insinuated that the former vice-president used his influence to help son Hunter Biden in his private-sector dealings in Ukraine, where he served on the board of an energy company.

Claims of Biden corruption have been fact-checked and largely debunked, but Trump has hammered away with his accusations in a thinly-veiled effort to cripple the Democratic frontrunner.

‘Joe Biden and his son are corrupt,’ Trump bellowed Tuesday.

If the accusations sounded worrying for Biden, his team suggested Democratic voters see it differently.

‘It's been our best week of fund-raising since the second week of the campaign,’ a campaign official told AFP Friday.

Biden himself has punched back against Trump. But in a Wednesday statement he said he ‘will continue to focus my campaign not on how Donald Trump abused his power to come after my family, but on how he has turned his back on America's families.’

Attacks on relatives of politicians is tricky business, and there is always the threat of a backfire. Voters may sympathize with Biden, who lost son Beau to cancer, and with Hunter, who has struggled with drug abuse.

Democrats have repeatedly savaged Trump's adult children, particularly sons Donald Jr and Eric, for their business dealings and campaign efforts.

Experts are split on how the Ukraine imbroglio will impact Biden, with American University professor of government David Lublin arguing it could serve Trump's rival well in the long run.

‘I can't imagine a better way to increase your support among Democrats than to be attacked repeatedly by Donald Trump,’ Lublin told AFP.

With Biden's campaign flagging -- rival Elizabeth Warren leapfrogged him to take top spot in recent polls in early voting Iowa and New Hampshire, as well as California -- a war of words with Trump could boost Biden's profile as a fighter and seasoned statesman.

- 'Guilt by association?' -

It could also bolster his campaign by siphoning attention away from Democratic hopefuls struggling to make their voices heard.

‘If you're not being talked about by the national news media, you don't exist,’ Lublin said.

Exhibit A: the president himself. Exhaustive news coverage of Trump in 2015 was largely negative, but it served to ‘crowd out coverage of his primary opponents,’ Lublin said.

There has been no proof of Biden wrongdoing, but the Trump narrative ‘is already taking hold,’ observed Seth McKee, associate professor of political science at Texas Tech University.

Trump has said Biden pressed for the removal of a Ukrainian prosecutor in order to protect his son, accusations dismissed by Democrats.

While Hunter's activities may not have been illegal, any appearance of a conflict of interest between his business dealings and his well-placed father could rub off on the candidate.

‘It's guilt by association,’ according to McKee.

By launching impeachment proceedings, House Speaker Nancy Pelosi has assured a steady focus on the Ukraine scandal, and by extension the conduct of the Bidens.

‘I don't see how that's a winner’ for Biden, McKee added.

‘You can circle the wagons and defend your son, but when you're on defense in politics it's never a good thing.’

Biden could benefit by appearing as the presumed nominee under attack by the president, said Tim Hagle, a University of Iowa professor who has long studied US politics.

But if Warren continues to surge, and voters question Biden's electability, problems could mount for him.

‘The bottom line here is... it's still a little bit early to tell whether this is going to be a help or a hindrance to Biden,’ Hagle said. ‘The fact that people are asking these questions (about Biden conduct in Ukraine) certainly can't help.’