“To the extent that Mayor Bloomberg is investing heavily in campaign ads in states that we have to win in the Electoral College and that those ads criticize or challenge President Trump’s values and his record and present a Democratic alternative, I think that’s a constructive thing,” said Sen. Chris Coons (D-Del.), one of five senators to endorse Biden.

Coons recalled in an interview that he recently saw three Bloomberg ads in an hour while watching the evening news and “Jeopardy” at his home in Wilmington, Del. — where the state primary isn’t held until the end of April.

The balancing act on Bloomberg comes as most Senate Democrats have opted to stay out of the 2020 campaign, saying it's too early to make a decision and that they’ll support whoever wins the nomination. They also may see little upside in opposing a Senate colleague in a race that still seems fluid or criticizing Bloomberg, a deep-pocketed donor who is making the case against Trump and could boost their party’s chances of seizing control of the Senate.

Sen. Doug Jones of Alabama, the most vulnerable Democrat in the Senate and another Biden supporter, said he finds Bloomberg’s ads helpful for his own campaign as they align with his focus on health care and jobs.

“These are not just slash and burn negative ads about the president, but just calling people’s attention to the fact that not all these presidential things are good for Alabama,” Jones said in an interview.

Since late November, the former New York mayor has spent more than $300 million on television and radio ads, and another $70 million on digital, according to numbers from Advertising Analytics. He is running ads in 27 states, including red states that Trump easily won in 2016 like Alabama, as well as purple states like Arizona, Colorado and North Carolina, according to his spokesperson.

Bloomberg’s 2020 rivals are, not surprisingly, frustrated with the billionaire’s ad buys.

Sens. Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt) have both accused Bloomberg of trying to buy the election. In a tweet ahead of Wednesday's debate, Warren wrote "it’s a shame Mike Bloomberg can buy his way into the debate" and described him as an "egomaniac billionaire."

But not everyone is complaining. Even those in the party who have long pushed for reforms to the campaign finance system argue they shouldn’t tie their hands — especially when it comes to taking on Trump.

“Anytime you can point out what’s going on in this administration, I think it helps Democrats… Bloomberg is helping to point out some of the challenges that this country’s having,” said Sen. Jon Tester (D-Mont.), a frequent critic of money in politics. “If you want to win, you gotta play the game that’s on the field. Do I wish we could change the rules of that game? You bet.”

“I welcome it,” added Sen. Sheldon Whitehouse (D-R.I.)., when asked about Bloomberg’s ads. “There’s a voice countering the big donors on the Republican side who are relentlessly forcing their trash out through Fox News and other...media.”

Bloomberg’s philanthropy has also won him fans in the caucus.

Sen. Ben Cardin (D-Md.), who emphasized he is not endorsing at this stage of the contest, said he admires that Bloomberg is “committed to using his resources” to elect a Democratic president and said his work in Baltimore to curb gun violence and invest in Johns Hopkins University gives him credibility in Maryland.

Sen. Chris Murphy (D-Conn.) described Bloomberg as a “force for good on the issue of gun violence.”

“There’s part of me that likes the fact that an anti-gun-violence champion is running for president,” Murphy said, adding, “There’s part of me that doesn’t want him to lose the focus that he had on the movement.”

Bloomberg has also opened up his wallet in the battle for the Senate, which senators surely haven’t forgotten.

In 2018, he donated $20 million to the Senate Majority PAC, a Democratic leadership-backed group trying to take back the Senate. He’s also donated to individual Senate Democrats over the years, including Ed Markey of Massachusetts and Jeanne Shaheen of New Hampshire — both of whom are up this year — as well as several Republican senators including John McCain of Arizona, Pat Toomey of Pennsylvania and Susan Collins of Maine, according to the Center for Responsive Politics.

Sen. Joe Manchin — a moderate from West Virginia who has said he is open to endorsing Trump — said the former New York mayor "looks like a responsible adult" but didn't say whether he would back him.

Bloomberg’s candidacy has stirred up opposition on the left. Nominating a billionaire former Republican who spent years defending stop-and-frisk policing policies will not sit well with progressives.

But for now, most Senate Democrats agree that his ads, particularly on health care, are helpful to their cause.

“Trump gets all this free publicity,” said Sen. Sherrod Brown (D-Ohio). “On health care, every Democrat wants universal coverage but at different speeds. Trump wants to basically take it away. … It’s whose side are you on — and Bloomberg’s ads are doing that. I do like that part about him.”

When asked whether he has any qualms about Bloomberg’s status as a billionaire buying air time, Brown said: “I’m glad he’s doing the ads, let’s leave it at that.”