Booker’s can’t-we-all-get-along retreat from his Clintonian past continued in the third debate, in September. Asked again about scrapping private health insurance, he replied, “I believe in Medicare for All” and then suggested that the debate didn’t really matter, because “every one of my colleagues on this stage is in favor of universal health coverage and comes at this with the best of intentions.”

Read: The 2020 U.S. presidential race: A cheat sheet

It’s easy to see why Booker adopted this tack. Conventional wisdom holds that candidates who go negative hurt themselves even when they draw blood. Moreover, during the summer and early fall, Warren rose from the pack to draw even with Biden nationally and surpass him in Iowa, thus confirming the widespread perception that Democratic voters were hungering for an ambitious, unapologetic progressive.

But as Warren rose, so did a backlash among Democratic donors and officials who saw her economic policies as dangerously radical and feared that she could not defeat Trump. As Biden careened from poor performance to poor performance, they began searching in earnest for an alternative. Booker might have been it. He was better known to party and financial elites than centrists such as Klobuchar, Bennet, and Montana Governor Steve Bullock; possessed more star power; and offered a greater chance of putting together the coalition of black and relatively moderate white voters that usually powers successful Democratic presidential campaigns. Unlike Kamala Harris, another African American senator who is more moderate than Sanders and Warren, Booker also had a long record of making the very arguments for a pro-business, deficit-conscious liberalism that the Democratic elites who feared Warren and Sanders craved.

Yet Booker refused to play that role. And that refusal helped Pete Buttigieg step into the breach. Initially, Buttigieg’s rise was powered less by ideology than by persona. His first breakthrough came during a CNN town-hall appearance in March. By spring, his novel combination of talents and attributes—gay, veteran, religious, midwestern, hyper-educated, dazzlingly articulate—was attracting comparisons to another political unicorn, Barack Obama. But after rising into the mid-single digits in national polls in April, Buttigieg plateaued through the summer and into the fall. As late as September, he still trailed Biden, Warren, and Sanders in both Iowa and New Hampshire by double digits.

Buttigieg’s initial breakthrough came less with voters than with donors. After initially making inroads among LGBTQ contributors, he emerged over the summer as the undisputed darling of the very money people who might have been Booker’s natural base of support. In June, a New York Times headline announced that “Wall Street Donors Are Swooning for Mayor Pete.” Buttigieg wasn’t yet attacking Sanders and Warren’s left-populist agenda. But by embracing big-donor fundraisers, which they eschewed, he signaled that he’d give pro-business Democrats a seat at the table. And in the absence of a compelling, avowedly centrist candidate, that was enough. As one finance-industry lobbyist told The Washington Post, “I don’t think Wall Street has a real great sense of what Mayor Pete might mean or not mean. But we do know what Warren means, and so I want part of every story about her to also be about him moving in tandem up the line.”