If Democratic U.S. Rep. Dean Phillips intends to mount a serious primary challenge against President Joe Biden, he must decide soon.

Phillips missed a Monday deadline to file as a candidate for the Nevada presidential preference primary election, meaning he won't be on the ballot in that early-voting state if he chooses to run. The Minnesota Democrat has blown past his self-imposed September time frame to decide whether to challenge Biden. His reluctance to make a decision so far has now put him at a disadvantage in a potential contest against Biden.

"What that indicates is that he is not serious about becoming the nominee, but if he does run, he wants to send a message to the party," Carleton College political science Prof. Steven Schier said of Phillips missing the Nevada deadline.

More primary election filing deadlines are approaching, including in the closely watched state of New Hampshire on Oct. 27.

Asked about Phillips potentially running a primary against Biden, New Hampshire Democratic U.S. Rep. Annie Kuster told the Star Tribune, "I think it's the best thing Donald Trump could ever ask for."

"There's no path. There's no outcry," Kuster said. "Personally, I think it's a vanity project by Mr. Phillips, and I think it could do serious damage by emboldening the Trump Republicans."

In a text message to the Star Tribune, Phillips acknowledged that he did not file for Nevada's primary but declined to elaborate further. He did not comment on recent criticism about a possible Democratic presidential primary run.

Phillips, in his third term in the U.S. House, came into this year with the potential of a bright political future. After ousting an incumbent Republican in the 2018 midterms, Phillips easily won re-election in his last two contests. He then won a spot in House Democratic leadership for the current Congress.

But the move by Phillips to scrutinize Biden's 2024 re-election run has isolated him both from Minnesota Democrats and his own party on Capitol Hill. Phillips confirmed earlier this month he was leaving his House leadership post, and he's publicly wavered over the past couple of months about whether he will make a longshot presidential bid.

Minnesota Democratic National Committee member Ron Harris has already announced a run for Phillips' congressional seat, underlining the pushback Phillips is encountering in his lonely stand questioning the wisdom of lining up behind Biden's 2024 campaign.

Phillips has made it clear that he will support Biden if the incumbent is the Democratic nominee.

But there's real fear among Democrats that what Phillips is doing could weaken Biden and help Republican Donald Trump return to the White House. Trump is making a third straight White House run while being charged in several criminal cases this year, including over the failed attempt to overturn the 2020 presidential election.

Phillips is personally wealthy, but his main campaign account didn't get a fundraising pickup as he publicly raised the prospect of running for the White House. A federal campaign finance report covering the start of July to the end of September shows Phillips' House campaign brought in only around $213,000 and had nearly $302,000 in campaign cash. His campaign also carried $250,000 in debt from a loan Phillips gave to his own campaign in 2018, the federal report shows.

"The fact that he's been making this noise may have actually hurt his fundraising in the district," Schier said.

Recent political history also shows that a primary challenge against a sitting incumbent is likely doomed.

Politico reported last week that Phillips has reached out to Democrats in New Hampshire. But Phillips' move to skip Nevada has added more confusion to the questions surrounding the Minnesotan's thought process — what exactly is Phillips trying to do?

"In the past couple of weeks, I have never come across so many New Hampshire Democrats who are angry that there's a sitting member of Congress who may actually contribute toward division in the Democratic Party and ultimately help elect Donald Trump," said Jim Demers, a prominent figure in New Hampshire Democratic politics and a Biden supporter.