BURLINGTON, Vt. — Vermont Sen. Bernie Sanders said Wednesday he’ll campaign actively this fall to send Democrat Hillary Clinton to the White House and bolster the party’s congressional candidates, with swings already planned in New Hampshire, New York and Washington state.

And while he has policy disagreements with Clinton, Sanders urged those who backed his bid for the Democratic presidential nomination to not defect to the Green Party’s Jill Stein or Libertarian Gary Johnson.

“Politics is tough stuff, and you’ve got to make difficult choices,” Sanders, an independent, told The Associated Press. “To me this was not a particularly difficult choice. Donald Trump would be a disaster for everything I believe in and I think my supporters believe in.”

Sanders called Trump “the worst candidate of a major political party in my lifetime.”

Speaking in his Burlington office, Sanders said it is important that Democrats regain control of the Senate.

“I think there’s a reasonable chance that that can happen,” Sanders said. “I’ll be as active as I can.”

He said he had already scheduled an appearance at an AFL-CIO breakfast in New Hampshire on Labor Day for both Clinton and Gov. Maggie Hassan, who is seeking to replace Republican Sen. Kelly Ayotte.

He said he also would campaign for Democratic House candidates in New York and Washington state.

“In our campaign there was an enormous amount of energy and grassroots activism,” Sanders said.

“Obviously I do not want to see that dissipate. I want to see that level of energy continue, at all levels of government from the school board to the United States Senate.”