First came the revelation that US President Donald Trump had encouraged the President of Ukraine to dig up dirt on Biden and his businessman son Hunter.

Then there House Speaker Nancy Pelosi's announcement that Democrats would launch an official impeachment inquiry against Trump to punish him for his conduct in the Ukraine affair.

Trump's doing this because he knows I will beat him like a drum.

Democratic presidential aspirant Joe Biden

Biden has tried to turn the issue to his advantage, using it to reinforce his central pitch to Democratic primary voters: I'm the candidate with the best chance of beating Donald Trump.

The President's willingness to engage in such risky behaviour, Biden argues, shows how scared he is going head to head with him in 2020.

"Why is he on the phone with a foreign leader, trying to intimidate a foreign leader?" Biden asked during the week.

"Trump's doing this because he knows I will beat him like a drum."

Some strategists believe the controversy will rally Democratic support behind Biden.

Most of the party's voters believe he is the victim of an unfair smear campaign, and don't want to see Trump rewarded for underhanded tactics.

But it's still far from guaranteed that the impeachment drama will work to Biden's benefit. It could also cement the emerging view that the 76-year old is a deeply flawed candidate whose best days are behind him.

It gives Trump ammunition to say that Biden is part of the swamp he is cleaning up.

Democratic strategist Hank Sheinkopf

"This is 'crooked Hillary' stuff," says veteran Democratic strategist Hank Sheinkopf, referring to Trump's favourite nickname for his 2016 rival.

"She had the email server, he has Ukraine.

"It gives Trump ammunition to say that Biden is part of the swamp he is cleaning up."

Hunter Biden served on the board of Burisma Holdings, a major Ukrainian natural gas producer, during the time his father was vice-president. Trump claims that Joe Biden sought the firing of a Ukrainian prosecutor to protect his son.

There is no evidence for the allegation that Biden inappropriately tried to get the prosecutor fired - western governments and multinational institutions agreed he was soft on corruption and needed to go.

But the lingering perception that Hunter Biden was getting rich overseas thanks to his dad's powerful position is a bad look.

Trump's re-election campaign is already spending millions of dollars on advertisements suggesting Biden is as dodgy as Hillary Clinton.

Even Democrats who think this isn't fair will be tempted to opt for a candidate who isn't vulnerable to such attacks.

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And Biden's claim that Trump is terrified to face him in an election is undercut by his own unimpressive performance so far on the campaign trail and the first three rounds of debates.

Ultimately Sheinkopf does not believe that the impeachment issue will upend the existing fundamentals of the Democratic primary.

"It's not enough right now to tell Democratic voters that if you win you'll make everyone feel better and make a few changes to the system," he says.

"It looks like Joe Biden is clinging to a centre that no longer exists."

The momentum, he says, remains with Warren.