MIAMI — Utah Sen. Mike Lee plans to endorse Texas Sen. Ted Cruz Thursday, making him the first U.S. senator to back Cruz’s presidential bid, sources told POLITICO.In a blow to Florida Sen. Marco Rubio, whose campaign is on life support as he seeks to avoid a knock-out blow in his home state Tuesday, Lee is expected to make the announcement in Rubio’s hometown of Miami ahead of Thursday night’s GOP debate.Lee is close with both senators, and he had resisted jumping into the race and potentially alienating one of them.