Drew Angerer / Getty Images Sen. Mike Lee (R-Utah) during an "Exempt America from Obamacare" rally, on Capitol Hill, September 10, 2013 in Washington, DC.

Utah Senator Mike Lee is not preparing for a possible presidential campaign, headlining the Iowa GOP Reagan Dinner this Friday, or landing the cover of national magazines. He is not the face of the Defund Obamacare movement. He is not Texas Senator Ted Cruz.

But Mike Lee is—and Cruz is not—the understated, policy-oriented leader behind the Defund Obamacare movement, according to several conservative leaders who spoke to TIME. He’s also one of the biggest hammers driving the wedge in the national Republican party to establishment and moderate Republicans. And to supporters of the health care law, like Majority Leader Harry Reid, he’s “living in a dreamland.” Given Lee’s influence on Defund Obamacare, and the resulting government shutdown, he is also a person whose national stature may soon rise to match his influence.

The story of the government shutdown began, for all practical purposes, in mid-Summer. “The big pivotal point was July 2,” says Lee’s spokemsan, Brian Phillips, when the Obama administration announced that it would not penalize businesses that do not provide health insurance in 2014. “It opened up a new door and perhaps a new front in the effort to stop Obamacare,” said Phillips. “We wanted to jump on it.”

The Senate Republican leadership had released statements hammering the President for delaying the employer mandate while leaving the individual mandate in place. But Lee took it one step further. On July 9, he released a statement laying out the strategy the House Republican leadership later adopted: fund everything but Obamacare in the bill that needs to pass by October 1 to keep the government open. He challenged congressional Democrats to shut it down, and then worked behind the scenes at the Republican conference lunches to garner support for defunding Obamacare. At the time, the press was largely focused on the turmoil in Egypt, Texas Gov. Rick Perry’s choice to not seek another term, and filibuster reform. Two days later, Cruz introduced a bill with 29 other Republican senators to fully defund the Affordable Care Act. But it was Lee who orchestrated the outside the beltway response that would bring Washington to its knees.

On July 17, three months before Sens. Mitch McConnell and Reid forged a deal to open the government and avert default, Lee welcomed the conservative leaders of national grassroots organizations into his office after-hours to discuss tying government funding to the Obamacare battles. Sens. Cruz, Mike Enzi, Jeff Flake, Jim Inhofe, Ron Johnson, Jim Risch, Marco Rubio, and Pat Toomey were in attendance, as well as representatives of Tea Party Patriots, FreedomWorks, and other conservative groups. The room was “packed,” said Jenny Beth Martin, President of Tea Party Patriots. Lee spoke first, led the discussion, and asked for support.

“That was the moment that brought everyone together,” said L. Brent Bozell III, the founder of the Media Research Center and a participant in the meeting. Bozell said that every outside group agreed with the strategy, and only one senator openly questioned the shutdown or defund tactic. “Mike Lee is the intellectual powerhouse of this entire movement,” added Bozell.

“It was something we were all eager to participate in out of conviction to the cause and respect for the great leader that Mike is,” said Heritage Action CEO Mike Needham, who also met with Lee in July.

Martin realized that there were some Republicans who might be open to a last-minute compromise. “One reason I felt so compelled to say they had to stay strong and not back down is because Rubio was in the room,” Martin told TIME. “Our coordinators from around the entire country were so frustrated with the way that Rubio acted during the Gang of Eight process. I wanted to make sure all of the senators who were in there knew where we stood, and especially he knew where we stood.” Rubio eventually voted against the Reid-McConnell deal reopening the government.

With the backing of grassroots conservatives, Lee announced on July 25 with 13 Republican senators that they would not support a continuing resolution that would fund further implementation or enforcement of Obamacare. On July 31, Heritage Action proclaimed a nine-city “Defund Obamacare Tour” featuring Needham, Heritage Foundation President Jim DeMint, and Cruz in Dallas. Despite the Republican leadership’s opposition, Lee and Cruz convinced enough congressmen by the end of September to use the threat of a government shutdown as leverage against already sequester-weary Democrats.

“What we did in those two months made all the difference,” said Phillips. “It was clear that at that point we had gone to our constituents, the American people, to the media, and had made the case over the last two months that this needed to be our stand.”

“I don’t think it would have happened but for that meeting,” added Bozell.

While Cruz stole the national spotlight, the most conservative wing of the GOP continues to sing Sen. Lee’s praises. “Senator Lee has been a tireless advocate for advancing the fight against Obamacare,” said Enzi, a Wyoming Republican. “Like many of us, he recognizes that the president’s health care law is a raw deal for the country and that it must be repealed, defunded, or dismantled piece-by-piece.”

“In my judgment there is no Senator in this body, Republican or Democrat, who is more principled, who is more dedicated, who is more fearless and willing to fight for the principles that make this nation great than is Senator Mike Lee,” said Cruz during his infamous 21-hour speech a few days before the shutdown. “I think over time you’re going to see more Mike Lees and fewer John McCains in the Republican Party,” Matt Kibbe, the President of FreedomWorks, told TIME. “And that’s a huge upgrade.”

But Lee’s judgement has also been called into question. After the 16-day partial government shutdown, at a cost up to $24 billion, Obamacare emerged unscathed. As a result, the strategy Lee orchestrated with Cruz and others has met a fierce backlash. Sen. Kelly Ayotte (R-N.H.) told TIME last week that she never received an answer from Lee or any Defund Obamacare supporter about how the plan was supposed to accomplish its goal. “The fact that the exchanges opened with the government shut down demonstrates on its face that it was not going to succeed,” said Ayotte.

Even Sen. David Vitter (La.), who says he’s “going to look for every opportunity to stop, or scale back, or delay, or postpone or repeal Obamacare,” told TIME he can’t confidently say how successful the strategy was, or what the next step will be. “I don’t know if we accomplished anything regarding that goal,” said Vitter, referring to actually defunding the health care act.

Other establishment Republicans have grumbled that the idea was misguided from the start. “A number of us were saying back in July that this strategy could not and would not work, and of course it didn’t,” said McConnell on Face the Nation. “There will not be another government shutdown. You can count on that.”

“We didn’t do anything except create a big mess in Washington,” said Sen. Tom Coburn (R-Okla.) on Meet the Press. “I’m not so inclined to think it was the Tea Party as much as it was outside interest groups and a few individuals within our party who took advantage of that situation.”

After the third longest government shutdown in 37 years, the question that remains is what will happen to Lee and the Republican Party. A CNN poll released Monday reports that 54% of Americans believe that Republican control of the House is bad for the country, up 11 points from mid-December. The latest Utah poll shows a 10% drop in Lee’s favorability, but the effects on the national GOP are likelier to be larger than those on Lee.

Utah has a caucus and convention candidate nominating system that favors Lee. “His voter market is only the base of the base,” says Mike Murphy, a Republican consultant who has advised several presidential campaigns. “I think it could be helpful to him, but only in the Tea Party silo of the GOP that he already has some support for. In the wider electorate, it hurts him more than helps him. But since Utah is not a swing state, my guess is he doesn’t care.”

Of course, Lee sees his efforts in a different light. “It’s always worth it to do the right thing,” Lee said on the Senate floor as Reid and McConnell put forward the deal which largely kept the status quo. “Some say we shouldn’t have fought because we couldn’t win, but this country wasn’t built by fighting when victory was absolutely certain.”