Bill ClintonWilliam (Bill) Jefferson ClintonKentucky candidate takes heat for tweeting he'd like to use congressman for target practice Will Sessions let other 'McCabes' off the hook or restore faith in justice? Progressive group launches anti-Trump 'We the Constitution' campaign MORE broke with President Barack ObamaBarack Hussein ObamaJudge orders Walker to hold special elections Mueller investigates, Peters quits Fox, White House leaks abound 2020 Dems compete for top campaign operatives MORE on Tuesday and endorsed Sen. Michael BennetMichael Farrand Bennet2020 Dems unify around assault weapons ban, putting pressure on colleagues McConnell, Schumer tap colleagues to explore budget reform Democrats march toward single-payer health care MORE’s (D-Colo.) primary challenger.

The former president sent out a fundraising appeal for Andrew Romanoff (D), who’s challenging Bennet in the Aug. 10 primary.

But by endorsing Romanoff, Clinton is going against the White House in one of the last competitive Democratic Senate primaries this cycle. Obama has raised money for Bennet’s reelection and made it clear his administration supports the incumbent.

The endorsement is surprising because Clinton had been seen as the White House’s problem-solver, having defused the controversy over the administration’s reported job offer to Rep. Joe Sestak (D-Pa.). It’s also rare for a party leader to back a primary challenger over an incumbent.

Romanoff, the former state House Speaker, endorsed Hillary ClintonHillary Diane Rodham ClintonWhite House would like to see Biden ‘in the boxing ring’ in 2020 House Judiciary chair subpoenas DOJ for FBI documents The suit to make Electoral College more ‘fair’ could make it worse MORE in the 2008 Democratic presidential campaign before Colorado’s caucuses, which Obama ended up winning.

Bennet’s campaign downplayed the news.

“The Clintons are known for their loyalty, so this doesn’t come as a huge surprise. Michael certainly doesn’t begrudge President Clinton the chance to thank a longtime friend,” Trevor Kincaid, a spokesman for Bennet, said in a statement.

The White House tried to discourage Romanoff from running. Last fall, Deputy White House Chief of Staff Jim Messina contacted Romanoff about a job he had applied for in the administration, but Romanoff opted to stay in the Senate race.

The Romanoff campaign said it doesn’t have any events scheduled with Clinton yet.

Clinton spokesman Matt McKenna told the Denver Post the fundraising e-mail would be the extent of the former president’s involvement in the race, but Romanoff said he’d like to see Clinton stump for him.

“I would certainly welcome that,” he told The Hill. Romanoff explained that the endorsement was in the works for only a short while. “This came together, really, over the last several days,” he said.

Clinton’s appearance on the stump could be a significant boost for the upstart challenger. Observers said the backing could help Romanoff raise much-needed money.

“It’ll give Andrew a bit of a boost. I don’t know how big of a boost, because frankly, you’ve got a lot of heavyweights committed on the other side,” said John Straayer, a political science professor at Colorado State University.

Romanoff has a “tremendous money deficiency,” he said. “Bill Clinton can raise money and the endorsement could help to some extent. This pushes the teeter-totter a little closer to even.”

Clinton is still popular in Colorado, he noted. “You’ve got to wait a little bit to see what the reaction is in the base of the party.”

As of March 31, Bennet had almost $3.6 million in the bank, while Romanoff had slightly more than $500,000.

Besides boosting Romanoff’s coffers, Clinton’s backing can help in other ways. Several strategists believe the former president to be a more highly coveted campaign surrogate than Obama.

Clinton’s already had an impact in the 2010 cycle. In May, he headlined an event for Rep. Mark Critz (D-Pa.) in the final days of Pennsylvania’s special election to fill the late Rep. John Murtha’s (D) congressional seat. Critz pulled off a somewhat unexpected win in the Republican-leaning district.

In early June, Clinton went to Arkansas to campaign for embattled Democratic Sen. Blanche Lincoln, who ended up winning her primary runoff.

His fundraising e-mail for Romanoff hit inboxes on Tuesday, the day before the end of the second-quarter fundraising period.

“We need Andrew’s leadership in Washington — especially now, when so many Americans are losing so much,” the former president wrote in his pitch to Romanoff’s supporters.

“ ‘It is not enough,’ as Andrew put it at the Colorado Democratic Assembly last month, ‘to put a president of real talent and vision and leadership in the White House if the same qualities are not matched at the other end of Pennsylvania Avenue.’ ”

That was the closest Clinton came to referencing Bennet. Bennet was appointed to the seat in January, after Obama tapped then-Sen. Ken Salazar (D-Colo.) to head the Interior Department.

Clinton said his relationship with Romanoff goes back to his student days.

“I first met Andrew Romanoff in 1992, when he was a student at the Kennedy School of Government and I was a candidate for president,” Clinton said in the e-mail. “Four years later, I was running for a second term, and he had just been elected to his first — as one of Colorado’s representatives on the Democratic National Committee.”
Clinton continued, “I was proud to carry Colorado in 1992, but you should be even prouder of what Andrew Romanoff did to turn the state blue. He worked harder than anyone in Colorado to put Democrats in positions of power — and to use that power to benefit every single citizen.”

He encouraged supporters to donate before Wednesday’s fundraising deadline. “Andrew won the state assembly by 21 points. With your help, he’ll win the primary and the general election,” Clinton wrote.

Outgunned financially, Romanoff has been waging a successful grassroots campaign.

He’s sailed through the state’s complicated nomination process, winning the precinct caucuses and county assemblies before winning the top line at the state convention.

The Bennet campaign has tried to downplay the significance of Romanoff’s success by noting that many candidates who win the party’s top line don’t go on to win the primary. The most recent example comes from 2004, when Democratic activist Mike Miles edged rival Ken Salazar at the Colorado Democratic convention for top position on the ballot, but lost to Salazar in the August primary.

Meanwhile, Obama has campaigned or raised money for four Democratic senators so far this cycle: Bennett, Barbara BoxerBarbara Levy BoxerThe ‘bang for the buck’ theory fueling Trump’s infrastructure plan Kamala Harris endorses Gavin Newsom for California governor Dems face hard choice for State of the Union response MORE (D-Calif.), Arlen Specter (D-Pa.) and Harry ReidHarry Mason ReidGOP pushes to change Senate rules for Trump Trump presses GOP to change Senate rules Only thing Defense’s UFO probe proves is power of political favors MORE (D-Nev.). He has a fundraiser planned for Missouri Senate candidate Robin Carnahan (D) in July.

Shane D’Aprile contributed to this article. 

This story was originally posted at 3:26 p.m. and updated at 8:35 p.m.