Sen. Bernie Sanders of Vermont speaking at the Democratic National Convention in Philadelphia in July. (J. Scott Applewhite/AP)

Sen. Bernie Sanders of Vermont is returning to the campaign trail next week, and he’s teeing off by asking his supporters to start putting their money into four Senate campaigns. In an email sent yesterday, Sanders encouraged donations to help Pennsylvania’s Katie McGinty, New Hampshire’s Maggie Hassan, Ohio’s Ted Strickland and Nevada’s Catherine Cortez Masto.

“I want to be clear: It is very important that our movement holds public officials accountable,” Sanders wrote in a message to his Friends of Bernie email list. “The Democratic Party passed an extremely progressive agenda at the convention. Our job is to make sure that platform is implemented. That will not happen without Democratic control of the Senate.”

Sanders previously endorsed Wisconsin’s Russ Feingold in his comeback bid. Recent polling has shown Feingold dominating that race, but Strickland has struggled to overcome attacks on his single gubernatorial term and just saw national Democrats cancel a planned ad buy.

In the email, Sanders offers a reason to back each newly endorsed candidate. McGinty “was one of the first candidates to endorse a $15 minimum wage,” while Hassan has been “a strong supporter of campaign finance reform.” Strickland is cited for opposing the Trans-Pacific Partnership, while Masto is credited for defending the environment and backing “equal pay for women.”

After this week, Sanders will also appear for Democratic candidates in person. That will represent the first rallies by the senator in support of downballot candidates since June 25, when he barnstormed western New York to help Eric Kingson, an academic and Social Security expert, in his bid for Congress. Kingson ran a strong second in the three-way primary.

After that, Sanders withdrew from view, emerging again to endorse Hillary Clinton and to speak at the Democratic National Convention last month in Philadelphia.

Now, Sanders’s ramp-up is centered on his email list — one of the largest in politics — and his new project, Our Revolution. Last Wednesday, at the Our Revolution launch event in Burlington, the environmentalist writer and activist Bill McKibben noted one of Sanders’s great selling points to Democrats.

As a result of his bid for the Democratic presidential nomination, which increased his exposure and made him a sort of blunt-talking celebrity, Sanders had become the sort of politician able to campaign anywhere.

“Bernie’s America’s most popular politician,” McKibben said. “Partly that’s down to his glamour and charisma; partly it’s down to the issues and ideas he’s come to embody, and that we’ll have to embody.”

Today, two of the candidates who hoped to embody that might hit the end of their reads. Rep. Alan Grayson (D-Fla.), who endorsed Sanders and positioned himself as the progressive in Florida’s U.S. Senate primary, is expected to lose after revelations about his messy divorce sent allies scrambling away from him.

And in south Florida, Rep. Debbie Wasserman Schultz (D-Fla.) is expected to defeat Tim Canova, an economics professor and former Capitol Hill staffer whom Sanders had made national news by endorsing. Canova, who faced a steep uphill climb in a district won by Hillary Clinton in the presidential primary, has complained publicly about Sanders’s decision not to campaign in the district. Pointedly, in his “Our Revolution” speech, Sanders rattled off a series of ballot initiatives and campaigns that he would be backing. He did not mention Canova, leaving his support of the campaign limited to an old fundraising email and a button on the Our Revolution page.