Carly Fiorina endorsed Republican presidential candidate Sen. Ted CruzRafael (Ted) Edward CruzOvernight Finance: GOP criticism of tax bill grows, but few no votes | Highlights from day two of markup | House votes to overturn joint-employer rule | Senate panel approves North Korean banking sanctions GOP criticism of tax bill grows, but few ready to vote against it Anti-gay marriage county clerk Kim Davis to seek reelection in Kentucky MORE (Texas) at a Miami rally on Wednesday, praising him as a political outsider.

"Ted Cruz has always been a constitutional conservative," the former Hewlett-Packard CEO said, describing Cruz as "a fearless fighter and reformer."

Fiorina ended her own White House bid in mid-February after a poor showing in early-voting states. 

Her campaign was known for her harsh criticism of Democratic presidential front-runner Hillary ClintonHillary Diane Rodham ClintonGOP rushes to cut ties to Moore Papadopoulos was in regular contact with Stephen Miller, helped edit Trump speech: report Bannon jokes Clinton got her ‘ass kicked’ in 2016 election MORE.

"The truth is that Donald TrumpDonald John TrumpDems win from coast to coast Falwell after Gillespie loss: 'DC should annex' Northern Virginia Dems see gains in Virginia's House of Delegates MORE and Hillary Clinton are two sides of the same coin," Fiorina said Wednesday, ripping the GOP front-runner. 

"They aren't going to reform the system. They are the system."

Fiorina noted that many in the Republican Party are "horrified by Donald Trump."

"I'm one of them," she added, describing Cruz as "the only guy who can beat Donald Trump."

"Ted Cruz has always been a constitutional conservative," Fiorina said, adding that he "didn’t care if he got invited to the cocktail parties in D.C."

Cruz complimented Fiorina as an "incredible business leader" in a press conference shortly after the endorsement.

"Her campaign for president impressed people all over this country, with her intelligence, knowledge, expertise ... with her ability to champion common sense conservative principles," Cruz said.

He pointed to Fiorina's support as "one more manifestation of what has been played out, as the one campaign that has demonstrated that can and repeatedly has beaten Donald Trump."

Cruz reiterated that rivals Marco RubioMarco Antonio RubioOvernight Cybersecurity: What we learned from Carter Page's House Intel testimony | House to mark up foreign intel reform law | FBI can't access Texas shooter's phone | Sessions to testify at hearing amid Russia scrutiny Cornyn: Senate GOP tax plan to be released Thursday This week: GOP seeks to advance tax overhaul MORE and John Kasich should "prayerfully reflect" and consider coalescing behind his campaign so he can go head-to-head with the front-runner. 

Both candidates are pinning their hopes on their home states, which hold their winner-take-all contests on March 15.

"If you want to stop Donald Trump ... unify behind our campaign," Cruz said, adding that Republicans "don’t want to hand the election to Hillary Clinton on a silver platter" in November.

Her endorsement comes the day after Cruz's primary victory in Idaho. But Trump swept up most of the states Tuesday night, including Mississippi, dealing a blow to the Texas senator in an important Southern state.

This brings Cruz's total number of states won to seven, while Trump has 15. Rubio lags far behind with only one victory in Minnesota, as well as the territory of Puerto Rico.

While Cruz still trails Trump in the overall delegate count, his victory in Idaho gives him bragging rights as the only candidate to best the GOP front-runner on Tuesday.

Cruz continues to position himself as the viable alternative to Trump and has called on his fellow GOP rivals to coalesce behind him.

Fiorina spoke about the GOP pushing for comprehensive immigration reform and trying not to "rock the boat" by shying away from social issues after failing to win the White House in 2012.

"It is time now to unite behind the one man who can beat Donald Trump, who can beat Hillary Clinton, who can beat the D.C. cartel. It is time to unite behind Ted Cruz," Fiorina said to roaring cheers.

Fiorina's support provides Cruz a feisty surrogate, who captured the spotlight in early debates by knocking Clinton and going after Planned Parenthood.

Fiorina, who mostly shied away from criticizing Cruz directly while she was in the GOP race, did accuse the Texas senator in January of saying "whatever he needs to say to get elected."

— Last updated at 12:28 p.m.