Wisconsin Gov. Scott Walker made it official Tuesday, endorsing Ted Cruz a week ahead of the state's pivotal Republican primary.

Cruz is "the best positioned by far" to defeat Donald Trump for the Republican presidential nomination and to win a general election over Democrat Hillary Clinton, Walker told Wisconsin radio talk show host Charlie Sykes.

"Ted Cruz is a principled constitutional conservative who understands that power belongs to the states -- and to the people -- and not bureaucrats in Washington," Walker said.

Cruz, who worked for the endorsement, has said he is "a big, big fan" of the governor, and that he is a "true conservative."

The endorsement of Cruz is not surprising. Walker said last week that Cruz is the only candidate who can beat Donald Trump, and Cruz previously tried to help Walker raise money to pay off his campaign debt.

Trump did not expect Walker's support, tweeting Tuesday: "After the way I beat Gov. Scott Walker (and Jeb, Rand, Marco and all others) in the Presidential Primaries, no way he would ever endorse me!"

It’s unclear how much the governor's endorsement will help Cruz, who is in a neck-and-neck race with Trump In Wisconsin, according to the RealClearPolitics average. Walker has been underwater on approval ratings in the Badger State for months.

Walker does remain popular among Republicans.

Charles Franklin, director of the Marquette Law School Poll, said his surveys show that, among GOP primary voters, Walker has a job approval rating of 77%.

Democrats mocked the Walker endorsement, citing the governor's criticism of public employee unions and education budget cuts as well as his failed presidential bid last year and low approval ratings.

"Now he’s lending that lack of support to Ted Cruz, a candidate every bit as extreme as Trump, but with the added bonus that he cost the economy $24 billion in a wasteful government shutdown -- fitting," said Luis Miranda, communications director for the Democratic National Committee.