The senators scored a win Friday when the Republican-led House, pushed by rambunctious rank-and-file members, passed a spending measure that would unravel the law. But the approach faces near-certain defeat in the Democratic-controlled Senate, where lawmakers in both parties complain that Cruz and Lee are pushing a losing cause.
In the meantime, their strategy has roiled many in the GOP, with plenty of public and private carping. House Speaker John Boehner, R-Ohio, subtly challenged Cruz and Lee to back up their words next week.
"I expect my Senate colleagues to be up for the battle," Boehner said.
Several Republicans say the tactic could lead to a government shutdown Oct. 1, the start of the new budget year, that would undercut the GOP politically as it faces a Democratic president weakened by perceived missteps on Syria.
They question Cruz and Lee's uncompromising approach, which has raised money for outside conservative groups and provided them with more than 1 million signatures on a "Defund It" petition; those are names that could be mined for future fundraising. Cruz's recent political moves have stirred talk of a 2016 presidential run.
Some Republicans privately fume that Cruz and Lee, stars of "Defund Obamacare" ads from the Senate Conservatives Fund, come off as the only two Republicans opposed to the health care law when in fact Republicans were united for months against Obama and the Democrats in trying to head off the law in 2009 and still vehemently oppose it.
The infighting, brutally on display in GOP primaries in Kentucky, South Carolina and Tennessee, could undermine the GOP's legitimate shot at winning a Senate majority next year. Twenty-one Democratic seats are on state ballots next year compared with 14 Republican. The GOP will need to gain six seats to win control of the chamber.
"I hate Obamacare," said Sen. Orrin Hatch, R-Utah. "I think it's one of the worst things that's been peddled off on America. I don't blame anybody for doing what they can to try to kill it, but there should be an end game."
Sen. Tom Coburn, R-Okla., called the combination of defunding "Obamacare" and the spending bill a "political ploy."
Lee said that although the conventional wisdom is Senate Majority Leader Harry Reid, D-Nev., has the votes to stop their effort, "in the meantime, those of us who feel strongly that Obamacare needs to be defunded will continue with our message."
In several fundraising appeals, Lee has warned that Obama, Democrats, the media and "even some from own party" are lying about his efforts to defund "Obamacare," saying he's trying to shut down the government. Not so, says Lee, who argues that he's trying to keep the government operating and end the health care law.