There's a movement among Capitol Hill Republicans to defund Obamacare. With the president's hugely expensive national health care scheme set to take effect Jan. 1, many of the law's opponents view this fall's battles over spending and the debt as the last chance to stop it, specifically by cutting off funds for its implementation.

But Republicans will not stop Obamacare. They won't defund it. Their last chance to put an end to it was the 2012 election. They lost, and the chance is gone.

On Thursday, Republican Sen. Mike Lee made public a letter pledging to "not support any continuing resolution or appropriations legislation that funds further implementation or enforcement of Obamacare." Citing the president's unilateral decision to postpone a major part of the bill, the employer mandate, Lee wrote, "If the administration will not enforce the law as written, then the American people should not be forced to fund it."

Money to fund Obamacare comes from two sources. A relatively small part of it, including some of the funds used to get the program going, comes from Congress' regular yearly appropriations. Congress could raise or lower the amounts without changing Obamacare itself. The defund-Obamacare Republicans in the Senate hope to strip out that discretionary funding from a continuing resolution needed to fund the government that Congress will debate in September.

They know they won't succeed. Democrats, with 54 votes, have enough to pass anything that requires a simple majority, and won't have much trouble getting to a filibuster-proof 60 votes, either. "I could count six or seven Republicans who would vote for full funding of the continuing resolution without breaking a sweat," says one Senate aide who supports defunding. "So they're going to get to 60."

But that's just the discretionary part of Obamacare. The far bigger portions of the program, including the billions and billions of dollars in subsidies that will start going to Americans on Jan. 1, are mandatory spending, an entitlement funded by an automatic appropriation which is written into law and runs without further congressional action. To change that, Congress would have to change Obamacare.

In the Senate, that would take 67 votes -- the amount needed to overcome a guaranteed presidential veto. If the 46 Senate Republicans voted unanimously to end the Obamacare entitlement, they would have to persuade 21 Democrats to go along.

The Senate Republicans advocating defunding know that's not going to happen. And since Senate Republicans are not even united themselves, they also don't have the power to shut down the government.

Of course, Republicans in the House do have the power to shut down the government, but even the most enthusiastic of the defund-Obamacare lawmakers in the Senate have real doubts as to whether Speaker John Boehner would do such a thing.

A shutdown would be "madness," says Douglas Holtz-Eakin, former head of the Congressional Budget Office who opposes Obamacare. "There is no exit strategy. It'll go on for a while, people will say Republicans shut down the government again, Republicans will cave, fund the government, and go on weakened and divided."

Some senators believe that if they could somehow shut off just the implementation funds, there would be no mechanism for the government to spend the mandatory money and, bingo, all of Obamacare would be effectively defunded. But Democrats thought of that back in 2009. A lot of Obamacare's implementation money comes from mandatory spending. It's going to flow no matter what, unless Republicans find those 67 votes.

So why the push? "We have to try," says the Senate aide. "Having this fight will show the people who sent us here that we are a party of principle. And after we lose this fight, all of our guys are going to have an issue that we can run on and win."

Of course, just 11 Republicans -- Rubio, Cruz, Risch, Paul, Inhofe, Vitter, Thune, Chiesa, Enzi, Fischer, and Grassley -- signed Sen. Lee's defunding pledge. That's about one-quarter of the Senate's Republican caucus. Undaunted, defunders say that big victories -- like the anti-gun control effort -- also started small.

But there's a difference between killing proposed legislation and stopping a law that is already in effect. And Republicans have run out of ways to stop Obamacare. The only way that will happen now is if the law proves to be a disaster that even its supporters abandon. Like everyone else, Republicans will just have to wait to see what happens.

Byron York, The Washington Examiner's chief political correspondent, can be contacted at His column appears on Tuesday and Friday on