Sen. Bernie Sanders will campaign for Montana Democratic congressional candidate Rob Quist in four cities over two days next weekend.

Sanders, who won the Democratic presidential primary in Montana over Hillary Clinton last year, will appear at rallies with Quist in Missoula, Butte, and Billings on Saturday, and in Bozeman on Sunday.

Quist, a musician, is positioning himself as a populist candidate in a vein similar to Sanders. He supports single-payer health care, wants to protect federally owned public lands in Montana, and has drawn attention to the fact that his opponent, Republican Greg Gianforte, is a millionaire like many other members of Congress.

Both candidates have pledged not to accept corporate PAC money, but Gianforte’s comments during a recent fundraising call raised the question of whether he was following through on that pledge, an allegation he denies.

GOP super PAC ads have tried to tie Quist to the national Democratic Party and Nancy Pelosi specifically, banking on the state’s Republican leaning. Inside Elections with Nathan L. Gonzales rates the district Republican Favored.

Quist recently turned down an offer of support from DNC Chair Tom Perez, keeping the national party at arm’s length.

Gianforte has enjoyed a lead throughout the race to represent Montana’s at-large congressional district, though a recent Democratic poll found Quist within 6 points of Gianforte.

Secretary of the Interior Ryan Zinke vacated the seat to join the Trump administration, setting up the special election.