House Democrats received some welcome news on Wednesday: Michael Bloomberg was coming to their rescue once again.

The former New York mayor announced he would spend $10m to protect vulnerable congressmen and women who have been on the receiving end of Republican attacks over their support for the impeachment inquiry.

Coming a little over a year after Democrats took back the House, partly thanks to a $100m infusion from Bloomberg, the announcement underscored the vast resources Bloomberg has at his disposal, even as he is using his $55bn fortune to launch a late bid for the Democratic presidential nomination.

The three-term mayor, who announced the start of his campaign less than three weeks ago, has already spent $100m on advertising in that race, far more than the four top-polling candidates combined. The only candidate who comes close is another billionaire, Tom Steyer. Bloomberg has hired hundreds of staffers, offering to pay field organizers $6,000 a month. Other campaigns pay $3,500.

The strategy to spend heavily and skip the first four states to vote, focusing instead on states like California and Texas that will vote on “Super Tuesday” in early March, has sparked complaints that the billionaire is trying to “buy” the nomination.

It is tone-deaf if Bloomberg actually thinks he can win a Democratic primary, let alone the presidential election Maria Langholz

Such gripes intensified after the withdrawal of the California senator Kamala Harris, who told supporters she did not have “the financial resources we need to continue”.

“I’m not a billionaire,” Harris said in a video explaining her decision. “I can’t fund my own campaign.”

Some of the most vocal critics of Bloomberg have been two of the most progressive candidates, senators Bernie Sanders and Elizabeth Warren.

Sanders said last month he was “disgusted by the idea that Michael Bloomberg or any other billionaire thinks they can circumvent the political process and spend tens of millions of dollars to buy our elections”. Warren has warned that elections should not be “for sale”.

In response Bloomberg argued his wealth would prevent him from being swayed by outside donations.

“I’m not buying anything,” Bloomberg told CBS. “I’m doing exactly the same thing they’re doing, except that I am using my own money. They’re using somebody else’s money and those other people expect something from them. Nobody gives you money if they don’t expect something. And I don’t want to be bought.”

Some of Bloomberg’s critics insist the mayor’s spending tactics could come back to haunt him with voters who are increasingly turning against the influence of money in politics.

“It is tone-deaf if Bloomberg actually thinks he can win a Democratic primary, let alone the presidential election,” said Maria Langholz, press secretary for the Progressive Change Campaign Committee, the first national group to endorse Warren.

“If you think about how Trump won, he railed against Wall Street interests, corporate trade deals and corruption in Washington – that appeals to the bases of both parties.”

Langholz argued that Bloomberg would only split the support of more moderate candidates like former vice-president Joe Biden and Pete Buttigieg, the mayor of South Bend, Indiana.

But a pair of new polls indicate Bloomberg may already be making more of an impact than many opponents who launched their campaigns several months before he did. According to the Monmouth and Quinnipiac polls, Bloomberg is at 5%, putting him in fifth place behind Biden, Sanders, Warren and Buttigieg.

Bloomberg meets Virginia house delegate-elect Nancy Guy at a coffee shop in Norfolk. Photograph: Drew Angerer/Getty Images

The Monmouth poll, however, also showed Bloomberg is not popular among the public at large, with more than twice as many registered voters viewing him negatively as positively.

Such numbers could prove to be a drag on Bloomberg’s campaign, considering he has based his bid around his supposed electability, telling voters America “cannot afford four more years of President Trump’s reckless and unethical actions”.

With that argument in mind, Bloomberg has promised to spend $100m on anti-Trump digital ads in six swing states, in addition to his campaign advertising.

Langholz predicted the mayor’s ads could serve to bolster his opponents.

“Given the amount he’s spending on ads, we’re watching to see if Bloomberg keeps his ads positive toward other Democrats and focuses his ire on Trump,” she said.

“If so, if he spends $100m making the case against Trump, that might actually yet again serve to help people like Warren and Sanders by making the entire field more electable against Trump.”