Four months after losing a bitter Democratic primary, and with less than a week before the presidential election, Bernie Sanders is doing much more than simply endorsing Hillary Clinton and serving as her surrogate. He’s crisscrossing the country, sometimes giving multiple speeches a day, whipping up crowds for his former rival and down-ballot Democrats alike. On Wednesday, demonstrating his willingness to make the case anywhere, his tour takes him to a city whose name is cultural shorthand for far-flung locales: Kalamazoo, Michigan.

It’s somewhat remarkable for the iconoclastic Vermont senator. Despite retaining his socialist ideals and opting again to return to Congress as a political independent, he is, at least for now, a partisan warrior.

“Bernie has demonstrated that he understands the stakes of this election,” Tad Devine, a Democratic consultant who was the senior strategist for Sanders’s presidential run, told The New Republic. He described his old boss campaigning for Clinton, which began in the summer, as “incredibly valuable” and “an enormous benefit for her” that “will have impact on Election Day.”

Sanders has never been a Democrat at heart. Back in February, PolitiFact delved into his career as a “40-year-outsider,” a rabble-rousing lefty who first ran for office with his state’s socialist Liberty Union Party, served as Burlington mayor as an independent and self-described socialist, and went to Congress, famously, with that same designation. Prior to 1990, he was actively hostile to Democrats, disparaging them in the press and running against them even when they warned he might play spoiler and help elect a Republican. (Madeleine May Kunin, the Democrat who was Vermont’s first female governor, says Sanders dismissed this concern before challenging her re-election in 1986; he called the two major parties “Tweedledum and Tweedledee.”)

Sanders did establish detente with the party after arriving on Capitol Hill—moving legislation, winning committee assignments, and even earning endorsements for re-election as the years progressed—but he never injected himself meaningfully into presidential politics. He attended his first Democratic National Convention eight years ago, backing Barack Obama in 2008 and 2012. But top Obama aides told BuzzFeed he didn’t lift a finger when it really mattered. In fact, he used to attack Obama from the left.

At the 2016 convention, Sanders was a star. After winning 23 primary contests and more than 13 million votes with an assault on the political establishment, he nevertheless acted to bring his followers into the fold. “Hillary Clinton must become the next president of the United States,” he declared unambiguously from the stage in Philadelphia. “The choice is not even close.”

Sanders’s strong support for Clinton, even though they “disagree on a number of issues,” is partly due to her genuinely moving in his direction on several policy issues—particularly his plan for tuition-free public colleges and universities, which she essentially embraced. Most of their “significant coming together,” as Sanders called it in his convention speech, came at the meeting of the Democratic Platform Committee, which produced, in the Vermonter’s words, “by far the most progressive platform in the history of the Democratic Party.”

“When the meeting had ended,” The Los Angeles Times reported, “Clinton had made several concessions to Sanders. The platform now calls for a $15-per-hour federal minimum wage, expansion of Social Security and setting a price on greenhouse gas emissions, positions that Sanders had embraced in contrast to Clinton’s more moderate stances during the primaries.”

In his speech, Sanders also noted, “the Democratic Party now calls for breaking up the major financial institutions on Wall Street and the passage of a 21st Century Glass-Steagall Act. It also calls for strong opposition to job-killing free trade agreements like the Trans-Pacific Partnership. Our job now is to see that platform implemented by a Democratic Senate, a Democratic House and a Hillary Clinton presidency—and I am going to do everything I can to make that happen.”

Sanders didn’t have to work too hard to convince his base to back Clinton. The “Bernie or Bust” mantra was overblown by the media, especially cable news. Most of his supporters aren’t Susan Sarandon. Even before the convention, Pew Research Center polling had found that, in the words of The Washington Post, “90 percent of unwavering Sanders supporters plan to vote for Clinton in November.”

Part of Sanders’s purpose as a team player this fall is to advance his agenda if Clinton becomes president. “Here’s what I’ll do the day after the election,” Sanders wrote in a recent Boston Globe op-ed, outlining his plans to do “everything possible to make certain that the new president and Congress implement the Democratic platform.” Chuck Schumer, likely the next majority leader if Democrats win the Senate, has said Sanders will “chair a significant committee if we win the majority. I don’t know which one it would be.’’

Campaigning for Clinton certainly improves Sanders’s standing with her administration if she wins, but Devine insists that’s not his goal. “I don’t think Bernie has done what he’s done in the campaign to get any kind of leverage in the next administration,” Devine said, but did acknowledge Sanders’s support “builds trust and communication.”

Journalist Harry Jaffe, author of the biography Why Bernie Sanders Matters, sees some strategic calculation. “I do believe he’s made the decision to play ball with the Democrats,” Jaffe told The New Republic, “and that will accrue to the benefit of what he hopes to accomplish.”

Of course, playing ball has its limits. As National Journal reported last year, Sanders has historically been “the curmudgeon in the Senate Democratic conference, rarely satisfied with how far his leadership will go to pursue progressive policies, and not afraid to vote ‘nay’ when his leaders come up short.” There’s no evidence he’d alter this approach with Clinton, and with a committee chair he’s been voicing his objections from a more powerful perch than in the past.

“When there’s not common ground he’s going to speak out very aggressively and boldly,” Devine said. “I don’t think you’re going to see him change. The guy doesn’t change a lot. I’ve known him for 20 years.”

Assuming Devine is right, Jaffe is correct to call Sanders’s union with Clinton and the Democratic Party “a marriage of convenience.” Considering the lovers quarrels to come after the election, that would make this week their honeymoon.