MIAMI (CBSMiami) – The plan concocted by Senators Marco Rubio, Ted Cruz, and Mike Lee to either defund the Affordable Care Act or shut down the government appears to be on its last leg after it passed the GOP-led House of Representatives last week.

The push to defund the ACA was championed throughout the summer by Senator Cruz. The Texas Senator called on the House to pass a continuing resolution that defunded the discretionary spending in the Affordable Care Act, or shut down the government.

After a week of back-and-forth, House leadership agreed to pass the continuing resolution with the defunding of the ACA attached. However, the CR only addresses discretionary spending and almost all of the ACA is mandatory spending. Plus, the White House can move money around to fill in any holes from a discretionary shutdown.

As the Senate prepares to act next, Cruz and his fellow tea party senators are in a unique position.

Senate Majority Leader Harry Reid will bring the House bill to the Senate floor with a motion to proceed. Republicans could filibuster this move, but they would be filibustering a bill that they support and trying to ensure a government shutdown.

If the GOP doesn’t filibuster when the bill is brought to the floor to proceed, Reid would propose an amendment to strip the ACA defunding from the bill and would only need a simple majority vote to pass the amendment.

The CR bill would then be subject to limiting debate, where Republicans could again filibuster. In order for Cruz to succeed in his pursuit of trying to shut down the government, he would need all 46 Republicans in the Senate to be unified with him to guarantee a filibuster of a bill that they support.

In other words, Cruz is asking for his fellow senators to filibuster a bill that the party asked to be passed by the House. Multiple GOP senators have said the defunding bill is bad policy and Cruz hasn’t made many allies in the Senate thanks to his antics during his first term in office.

“In the United States Senate, we will not repeal or defund Obamacare. We will not. And to think we can is not rational,” Sen. John McCain (R-AZ) said last Thursday on CNN. “To somehow think we are going to defund it is simply not going to happen at this time, and it will, in my opinion, as it did before, harm the American people’s view of the Republican party.”

“Tactics and strategies ought to be based on what the real world is. We do not have the political power to do this,” Sen. Tom Coburn (R-OK) said Sunday on CBS’ “Face The Nation.” “So we’re not about to shut the government down over the fact that we cannot, only controlling one house of Congress, tell the president that we’re not going to fund any portion of this [health care law]. Because we can’t do that.”

If Cruz managed to pull off a filibuster, he and his fellow Senators who upheld the filibuster would be on the hook for shutting down the government by filibustering a bill that they support.

If Senator Reid passes the continuing resolution funding the government at sequestration levels without stripping any discretionary funding from the Affordable Care Act; the action would return to the House of Representatives.

Once back in the House, the GOP leadership would have to either convince the more conservative members to support the bill at sequestration levels with the ACA intact, or turn to the Democratic members for help getting enough votes to finally approve the continuing resolution to fund the government.

Regardless of how this fight turns out, the tea party and its supporters are planning a secondary fight by threatening to default on the national debt in a few weeks if the ACA isn’t defunded. A debt default is considered by economists one of the worst things that can happen and could lead to devastation in the U.S. and global economy at a level never seen before.

If the tea party loses the government shutdown fight, the debt limit is the last stand. However, by that time, most of the ACA will already be in place making the fight that much less palatable to many fellow representatives and senators.