Montana Democratic Sen. Jon Tester, new chairman of the Democratic Senatorial Campaign Committee (DSCC), has flip-flopped from his previous support for the Keystone XL pipeline.

On Monday, Tester was one of the few Democrats who had previously supported the Keystone pipeline who voted against it when given the chance to vote on it.

“The legislation that would yank President Barack Obama’s authority over the pipeline on Monday lost a vote from one of its longtime backers, Sen. Jon Tester (D-Mont.) — now a member of party leadership as chief of the Democratic Senatorial Campaign Committee — but picked up a vote from Sen. Michael Bennet (D-Colo.), the former DSCC chairman who has not formally signed onto the pipeline bill,” Politico wrote after the Senate votes.

Tester hasn’t left much doubt about his support for the Keystone XL Pipeline. On his U.S. Senate webpage, Montanans can find a post titled: “Why I Support The Keystone XL Pipeline.”

“Building the Keystone XL pipeline will help Eastern Montana to reach its full economic potential,” Tester wrote in the post. “The pipeline would run through Montana and include an on-ramp in Baker for oil from the Bakken. The on-ramp will deliver up to 100,000 barrels of oil per day to market. Today, Bakken oil is getting less than market value because of shipping constraints — Keystone XL will help fix that.”

As recently as earlier this month, Tester said he would vote for the Keystone XL Pipeline. “I think the pipeline should be built,” Tester said in a Montana Public Radio interview broadcast on Jan. 5.

And I think if we do this right, it could take a lot of pressure off of middle eastern oil. Look, there’s negatives, too. I know the tar sands is one of the biggest emitters of CO2 there is, but by the same token, I think until we have the research and development out there to get us off of oil and give us other options, this is one of the options we have to do, and that’s to build the pipeline.

Now that Tester has flip-flopped, newly-elected Rep. Ryan Zinke (R-MT) was quick to criticize him.

“Montanans expect their lawmakers to do what they say, and say what they do,” Zinke said in a statement to Breitbart News. “To me, a vote against the Keystone is a vote against Montana. I’m a proud co-sponsor of the House bill to build the Keystone XL Pipeline because it is proven to be safe and in the best interest of Montana. I will always put Montana before raising money from special interests in Washington, D.C.”

Zinke, a retired Navy Seal, was elected to Montana’s at-large U.S. House seat, evidence he can win a statewide race in Montana. It’s highly likely Zinke, among other Republicans, will look at a run for U.S. Senate down the road when Tester comes up for re-election in 2018.