Republican presidential candidate Ted Cruz said the "full spectrum" of the Republican party is getting behind his campaign. Cruz was speaking at an event in New York March 23. (Reuters)

The can’t-quite-believe-what’s-happening shotgun marriage between Ted Cruz and the Republican establishment further solidified Wednesday when Jeb Bush endorsed the senator from Texas and Wisconsin Gov. Scott Walker signaled that he is also likely to back him.

Cruz’s growing roster of mainstream Republican support is a striking development for someone who has consistently sought in his political career and during his year-long campaign to portray himself as the ultimate Washington outsider.

But the senator has been far outdone on that score by Donald Trump, and now Cruz and mainstream Republicans have common cause in an urgent, mutual desire to prevent the New York billionaire from running away with the nomination.

Not that they are entirely comfortable with one another. Bush delivered his endorsement in a written statement, not a joint news conference or photo op. Cruz welcomed him but didn’t linger in praise.

In his statement, Bush called Cruz a “consistent, principled conservative who has demonstrated the ability to appeal to voters and win primary contests.”

He added: “For the sake of our party and country, we must move to overcome the divisiveness and vulgarity Donald Trump has brought into the political arena, or we will certainly lose our chance to defeat the Democratic nominee and reverse President Obama’s failed policies.”

In an interview with WTMJ radio in Wisconsin, Walker, a former presidential candidate who has stayed out of the national spotlight since ending his short-lived campaign in the fall, said he would probably make an endorsement before his state’s April 5 primary. He made clear that he thinks Cruz has a much better chance of winning than Ohio Gov. John Kasich, the only other non-Trump candidate left in the Republican race.

“You’ve pointed out that if you’re someone who’s uneasy with the front-runner, right now there’s only one candidate — I think if you’re just looking at the numbers objectively — Ted Cruz,” Walker told host Charlie Sykes in an interview recorded before Tuesday’s Arizona and Utah contests. “Senator Cruz is the only one who’s got a chance, other than Donald Trump, to win the nomination. My friend Governor Kasich cannot.”

Many fear that Bush’s support comes at a time when it is already too late to block Trump’s path to the nomination. He padded his wide lead in delegates with a win in Arizona on Tuesday. Cruz won Utah, which has fewer delegates.

Campaigning at the Women’s National Republican Club in Manhattan, Cruz ticked through a list of supporters he was won in the past 10 days, including Bush, Mitt Romney and Sen. Lindsey O. Graham (R-S.C.), all of whom have clashed sharply with the senator in the past.

“If you want to talk about the full spectrum of the Republican Party, as broad and ideologically diverse as you could imagine, that’s it,” Cruz said.

As Cruz read the three names, the crowd applauded. But their cheering was much louder when he mentioned Sen. Mike Lee (R-Utah), who, like Cruz, has clashed with party leaders.

Republican presidential candidate Sen. Ted Cruz (R-Tex.) offered his condolences to the victims in Brussels and said, "This is a war." (Reuters)

Cruz spokeswoman Catherine Frazier said she expected Bush to provide a fundraising boost to the campaign. With Trump mostly self-funding, Cruz’s financial team sees an opportunity for a much-needed replenishing of his campaign coffers.

“Our only competition, if you could call it that, is Kasich,” said Mica Mosbacher, a Texas-based Cruz fundraiser whose husband served as commerce secretary under President George H.W. Bush. Kasich has lagged behind in the money chase.

In the Senate, Cruz has caused headache after headache for GOP leaders. Many blamed his 2013 fight to shred Obamacare for a government shutdown. He called Senate Majority Leader Mitch McConnell (R-Ky.) a liar on the floor of the Senate. And he refused to back incumbent Republican senators against primary challengers in the 2014 midterm elections.

Ultimately, associates say, Bush, who ran as a centrist alternative to Cruz and others, made a pragmatic decision: Cruz is the only one left who can beat Trump.

“I think he made the endorsement because he felt Ted could be the best vehicle among those left to get the nomination,” said Charles Foster, a Houston lawyer and Cruz donor who supported Bush and is close to the Bush family.

The endorsement was finalized in a phone call between Cruz and Bush on Monday. They had met in person this month in Miami before a presidential debate there.

Despite the senator’s professional ties to former president George W. Bush — he worked for Bush’s 2000 campaign — Cruz and Jeb Bush have no personal or professional relationship despite meeting and chatting at presidential debates and their recent interactions.

But there is a notable link: Jeb’s son, George P. Bush.

The 39-year-old Texas land commissioner is now considered the Bush family’s next best hope to reclaim the White House, but he cannot expect to easily advance in Texas state politics without Cruz’s support.

At no time during their interactions was there any talk of how a Bush endorsement might affect the political future of George P. Bush, said associates of the governor familiar with the talks and the Cruz campaign. The Cruz campaign declined to comment on the interaction but did not dispute that account.

While Cruz has racked up establishment support in recent days, many would-be backers have not moved off the sidelines. Among them: Sen. Marco Rubio (R-Fla.) and many donors in his deep pool of financial support.

Some say they are waiting to see what happens in Wisconsin, where a Trump win could deal a decisive blow to Cruz and Kasich. Others say they doubt Cruz can win a general election.

“I don’t have too much concern about where he stands,” said Frank VanderSloot, an Idaho billionaire and top Rubio donor. “I have concerns about how he stands there. He comes across as arrogant.”

With Trump running as even more of an outsider than Cruz, there is some risk for the senator from Texas becoming too closely associated with mainstream figures.

“I think it hurts him,” Trump said in an interview with The Washington Post. “I think it actually hurts, and I don’t want those endorsements.”

O’Keefe reported from Washington. Katie Zezima in New York, Karen Tumulty in Palm Beach, Fla., and David Weigel in Waukesha, Wis., contributed to this report.