Now playing
01:19
Utah Sen. Mike Lee endorses Sen. Ted Cruz
Twitter / @smashracismdc
Now playing
01:50
Cruz swarmed by protesters at DC restaurant
ted cruz beto o'rourke split
Pool
ted cruz beto o'rourke split
Now playing
02:55
Ted Cruz, Beto O'Rourke spar in first debate
Senator Ted Cruz at a debate in Dallas, Texas.
Pool
Senator Ted Cruz at a debate in Dallas, Texas.
Now playing
01:20
Ted Cruz: Americans are 'Dreamers' also
BOONE, IA - JANUARY 4:   Republican presidential candidate U.S. Sen. Ted Cruz (R-TX) visits King's Christian Bookstore on January 4, 2016 in Boone, Iowa. Cruz began a six-day bus tour of Iowa ahead of the state's February 1, caucuses.  (Photo by Aaron P. Bernstein/Getty Images)
Aaron P. Bernstein/Getty Images North America/Getty Images
BOONE, IA - JANUARY 4: Republican presidential candidate U.S. Sen. Ted Cruz (R-TX) visits King's Christian Bookstore on January 4, 2016 in Boone, Iowa. Cruz began a six-day bus tour of Iowa ahead of the state's February 1, caucuses. (Photo by Aaron P. Bernstein/Getty Images)
Now playing
02:06
Ted Cruz speechless for 18 seconds after question
Facebook CEO Mark Zuckerberg arrives to testify before a joint hearing of the Commerce and Judiciary Committees on Capitol Hill in Washington, Tuesday, April 10, 2018, about the use of Facebook data to target American voters in the 2016 election. (AP Photo/Pablo Martinez Monsivais)
Pablo Martinez Monsivais/AP
Facebook CEO Mark Zuckerberg arrives to testify before a joint hearing of the Commerce and Judiciary Committees on Capitol Hill in Washington, Tuesday, April 10, 2018, about the use of Facebook data to target American voters in the 2016 election. (AP Photo/Pablo Martinez Monsivais)
Now playing
02:22
Cruz presses Zuckerberg on Facebook politics
Cuomo Cruz Split
Cuomo Cruz Split
Now playing
02:49
Cuomo presses Ted Cruz on his name change
ted cruz cpac gun sot _00000000.jpg
ted cruz cpac gun sot _00000000.jpg
Now playing
01:00
Ted Cruz: We should target criminals
ted cruz comments on 2013 shut down sot  _00001621.jpg
CNN
ted cruz comments on 2013 shut down sot _00001621.jpg
Now playing
01:40
Cruz: I have consistently opposed shutdowns
CNN
Now playing
00:55
Cruz: Grief after shooting staggers the mind
CNN
Now playing
01:37
Ted Cruz on the porn tweet: 'It was not me'
WASHINGTON, DC - MARCH 20:  U.S. Sen. Ted Cruz (R-TX) speaks during the first day of the Supreme Court confirmation hearing for Judge Neil Gorsuch before the Senate Judiciary Committee in the Hart Senate Office Building on Capitol Hill March 20, 2017 in Washington, DC.
Justin Sullivan/Getty Images
WASHINGTON, DC - MARCH 20: U.S. Sen. Ted Cruz (R-TX) speaks during the first day of the Supreme Court confirmation hearing for Judge Neil Gorsuch before the Senate Judiciary Committee in the Hart Senate Office Building on Capitol Hill March 20, 2017 in Washington, DC.
Now playing
01:39
Ted Cruz on health care: The math is simple
ted cruz sex toys dana bash intv sot_00003507.jpg
ted cruz sex toys dana bash intv sot_00003507.jpg
Now playing
01:13
Ted Cruz: The left seems obsessed with sex
CNN
Now playing
00:51
Porn video 'like' removed from Cruz's Twitter
cruz health care sot
CNN
cruz health care sot
Now playing
01:15
Cruz: Senators will face tough questions
ac zeleny who is ted cruz_00005407.jpg
ac zeleny who is ted cruz_00005407.jpg
Now playing
03:09
Who is Ted Cruz?

Story highlights

Utah Sen. Mike Lee endorsed Ted Cruz for president Thursday, making him the first senator to do so

Lee praised Cruz for the promises he has made to protect gun rights, fight Obamacare and uphold other conservative principles

Washington CNN —  

Utah Sen. Mike Lee endorsed Ted Cruz for president Thursday, making him the first senator to back the Texas lawmaker, and delivering another blow to Marco Rubio.

Lee praised Cruz for the promises he has made to protect gun rights, fight Obamacare and uphold other conservative principles, in an announcement just hours before CNN’s Republican debate.

“Ted has kept those promises and every other promise he has made to the people of Texas,” Lee said. “It is with that trust that he’s earned that he’s going to move forward and unite our party.”

The nod from the tea party favorite comes as Republican leaders have grappled with the reality that Cruz, not Rubio, appears best poised to defeat Donald Trump for the Republican nomination. It’s also notable because Cruz has alienated many GOP Senate colleagues over his tactics on legislation since entering the chamber in January 2013.

RELATED: Trump or Cruz? GOP leaders shake their heads, prepare to choose

The Texas senator picked up a big endorsement from former rival Carly Fiorina Wednesday, after she said she was “horrified” by Trump. And Sen. Lindsey Graham, a former Republican candidate, is leading the push to rally his colleagues and party leaders to get behind Cruz, based on the senator’s lengthy record as a Republican and his strong messaging skills.

But many Republican senators, like North Carolina’s Richard Burr, have said they would be open to supporting Trump.

Many establishment Republicans and lawmakers flocked to Rubio, the Florida senator. But his poor performances in recent contests have left them considering either Trump or Cruz – both of whom have built campaigns as Washington outsiders lambasting the Republican establishment.

CNN’s Manu Raju contributed to this report.