Walker said that he was “proud” to support Cruz during an interview with Wisconsin conservative talk show host Charlie Sykes, an anti-Trump Republican who hosted Donald Trump on his program Monday for a combative, often critical, interview.

In a series of tweets Tuesday morning, Walker explained his decision:

After the failed Obama-Clinton Admin, Americans want leadership. I endorse @TedCruz, a principled constitutional conservative who can win.

— Scott Walker (@ScottWalker) March 29, 2016

Like we did in WI, @TedCruz isn’t afraid to stand up to big govt special interests. He understands that power belongs to states, not Wash DC

— Scott Walker (@ScottWalker) March 29, 2016

.@TedCruz is the best-positioned candidate to both win the Republican nomination and defeat Hillary Clinton. I’m proud to stand with him.

— Scott Walker (@ScottWalker) March 29, 2016

The former primary candidate, who has consistently bashed Trump, was widely expected to endorse Cruz before he made his official announcement. In a taped interview with Sykes that aired last week, Walker hinted at his coming endorsement: “If you’re someone who is uneasy with the front-runner right now, there’s really only one candidate,” he said. “Ted Cruz is the only one who’s got a chance other than Donald Trump to win the nomination statistically, and my friend Gov. [John] Kasich cannot.”

Trump, who previously called Wisconsin a “disaster” under Walker, already had a response to the expected endorsement Monday night.

I have millions more votes/hundreds more dels than Cruz or Kasich, and yet am not being treated properly by the Republican Party or the RNC.

— Donald J. Trump (@realDonaldTrump) March 29, 2016

While polling data is sparse for Wisconsin, Cruz seems to have nearly closed Trump’s lead in the state, according to Politico.