Michael Bloomberg’s use of his vast fortune to gain the Democratic presidential nomination is unprecedented. There have been rich men who have sought and won high office before, notably Franklin D. Roosevelt, John Kennedy, and Nelson Rockefeller. But there is a crucial difference between those previous scions of wealth and Bloomberg. Previous rich politicians might have leveraged their wealth, but their political careers were restrained by party loyalty.

Roosevelt and Kennedy were lifelong Democrats, Rockefeller a Republican. Each of them rose to power by working with party regulars, creating a network through service, compromise, and negotiation. This meant a life of campaigning with party members and being attuned to party concerns. And when they disagreed with party decisions, as Rockefeller did with the nomination of Barry Goldwater in 1964, they had to pay a price. Rockefeller’s presidential hopes died with his feud with Goldwater.

Bloomberg is a political free agent, jumping from party to party as it suits his need. He was a Democrat before 2001, but became a Republican from 2001–07 so he could run for mayor of New York. He left the GOP in 2008 to become an independent, only rejoining the Democrats in 2018.

This history of shifting party membership obscures the fact that Bloomberg has always supported politicians of either party depending on how useful they are to him. In 2016, he was a major factor in the reelection of Senator Pat Toomey, giving the Pennsylvania Republican $12 million. In 2018, Bloomberg donated to then–New York Republican Representative Dan Donovan and hosted a fundraiser for Republican Peter King. He also endorsed Pennsylvania Republican Brian Fitzpatrick.

Bloomberg argues that he supported these Republicans because they are moderates on gun control. This argument makes clear that Bloomberg even now doesn’t see himself as a Democrat. Rather, Bloomberg is a special interest, a one-man lobby group, someone who can make use of the Democratic Party on occasion but can equally make use of the Republican Party.

There’s nothing wrong with being a special interest that backs either party. Historically, groups like Planned Parenthood and the ACLU have acted that way. But Bloomberg is a special interest who is running for president.

Perhaps the closest precedent for Bloomberg is Ross Perot, who spent $60 million running for president in 1992 and made another bid in 1996. Perot created his own vehicle, the Reform Party. That’s too much work for Bloomberg, who is trying to use his money to take over an existing party.

Bloomberg’s support within the party rests not just on the $400 million he’s spent in this election cycle and the promise of much more. It is also traceable to the billions in philanthropy he’s given in recent decades.

As The New York Times reported on Saturday, this spending has shifted the political landscape, with progressive groups beholden to Bloomberg’s largesse making themselves subservient to him. Feminist groups like Emily’s List, which might be expected to take umbrage at Bloomberg’s history of alleged sexual harassment and chauvinistic comments, have been muted in their criticism of the former New York City mayor. The Center for American Progress excised from a report on anti-Muslim bias a chapter that was critical of Bloomberg’s mayoral tenure.

The behavior of Emily’s List and the Center for American Progress indicate how Bloomberg’s ascendancy has come at the price of compromising progressive principles. As one of the richest men in the world and running a self-financed candidacy, Bloomberg would have the same effect on the Democratic Party if he becomes the standard-bearer. There would be no interest that could hold him in check, no group that he owes loyalty to.

What’s true of progressive organizations is also true of public officials. As The New York Times documents, officeholders who have benefited from Bloomberg’s donation have been quick to endorse him.

Bloomberg is creating a new model for running for president: one where a rich man can simply buy a political party as easily as he acquires a mansion or a yacht. In the words of columnist Damon Linker of This Week, Bloomberg is trying to “effectively purchase the institutional Democratic Party, absorb it into Bloomberg LP, and use this hybrid corporate-political enterprise to fulfill the fervent wish of Democratic voters to defeat Trump.”

One problem with this model is that it would negate the other major model for defeating Trump. Bernie Sanders and Elizabeth Warren have a theory of change very different from Bloomberg’s: They are using a small-donor army to fund their campaign, holding rallies, and trying to bring new people into the system.

As Greg Sargent of The Washington Post notes, “Sanders’s fundraising success is a truly monumental achievement. Sanders, like Warren, has forsworn both help from corporate PACs and high-dollar donations.” Sargent then asks, “What message will it send if Democrats allow this new model to be snuffed out under an avalanche of one billionaire’s spending from his plutocratic fortune?”

Sanders, like Bloomberg, can be accused of not being a party loyalist. But the difference is, Sanders is an insurgent trying to change the Democratic Party by creating a mass movement that could infuse it with new blood. Bloomberg wants to simply buy the existing party and make it an instrument for his personal ambition.

“The Bloomberg candidacy is nothing less than a self-destruct button for the Democratic Party,” Osita Nwanevu recently argued in The New Republic. Bloomberg’s nomination, he pointed out, would alienate wide swaths of the Democratic Party coalition, including anti-racists, economic populists, and feminists.

It’s possible that Bloomberg could win the nomination and the presidency. But if he does so, he will transform the very nature of the Democratic Party and also diminish, and possibly extinguish, the reform movements headed by Sanders and Warren.

Under Bloomberg, the Democrats would become the party of money, not the party of the many.