(CNN) The Republican Party's efforts to gut former President Barack Obama's legacy health care law came to an abrupt -- if temporary -- halt Monday night.

Just hours after the Senate was gaveled back into session, Senate Majority Leader Mitch McConnell was handed two more public defections on his health care bill to overhaul Obamacare. The dramatic and simultaneous announcement from Sens. Jerry Moran of Kansas and Mike Lee of Utah means McConnell officially does not have the votes to even begin debate on his legislation to overhaul the Affordable Care Act.

The development deals a devastating blow not only to Republicans who have railed against the law for years, but also President Donald Trump, who campaigned on killing Obamacare and made repealing the law his top legislative priority since taking office.

"Regretfully, it is now apparent that the effort to repeal and immediately replace the failure of Obamacare will not be successful," McConnell said in a statement late Monday. He said the Senate would vote in the coming days on a bill that would delay the repeal of Obamacare for two years -- all as Trump called for a wholesale repeal of the law.

In announcing their opposition to the bill, Moran and Lee said they would vote "no" on the motion to proceed -- a vote that McConnell had hoped to hold this week but was already forced to postpone due to Arizona Sen. John McCain's unexpected absence from Washington.

"We should not put our stamp of approval on bad policy. Furthermore, if we leave the federal government in control of everyday healthcare decisions, it is more likely that our healthcare system will devolve into a single-payer system, which would require a massive federal spending increase," Moran said in a statement.

The surprise announcement was all the more devastating as Trump was trying to shore up support for the bill at a dinner at the White House. The group of attendees included Sens. Richard Shelby of Alabama, Steve Daines of Montana and James Lankford of Oklahoma. The three, like Moran, are reliably conservative senators who generally vote with McConnell on major bills.

After Moran and Lee's announcement, Trump tweeted , "Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate. Dems will join in!"

Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate. Dems will join in! — Donald J. Trump (@realDonaldTrump) July 18, 2017

On Tuesday morning Trump returned to Twitter: "We were let down by all of the Democrats and a few Republicans. Most Republicans were loyal, terrific & worked really hard. We will return!"

In another tweet he added , "As I have always said, let ObamaCare fail and then come together and do a great healthcare plan. Stay tuned!"

In a stark sign of just how grave his concerns are about the bill, Moran went as far as to call for a "fresh" start and an "open legislative process."

McConnell's inability to convince the senators to hold off on publicly opposing the bill highlighted the huge chasm that had developed between the efforts of the leadership to pass a bill and the willingness of rank and file senators to agree to something they had serious reservations about.

Also in attendance at the White House gathering Monday night was Sen. Lamar Alexander of Tennessee, who chairs the Senate health committee and who has been heavily involved in crafting the bill. An aide told CNN before the meeting that even Alexander could not commit to voting for the bill.

In fact, an ongoing CNN whip count showed only a handful of Republicans fully supporting the bill, many of them members of the elected leadership and chairmen of other committees negotiating the bill.

The CNN count showed a whopping 41 of the 52 GOP senators unwilling to commit to either the motion to proceed on the bill, a key procedural vote to begin debate, or the bill itself.

Prior to Monday, there were two other Senate Republicans who had said they would vote against the revised health care bill: Sens. Rand Paul of Kentucky and Susan Collins of Maine. This meant McConnell could not afford even one more opposing senator.

Over the weekend, McCain's office revealed that the veteran senator had surgery to remove a blood clot from above his eye, forcing him to stay back at home in Arizona. Shy one "yes" vote on the motion to proceed, the majority leader announced that he would "defer" consideration of the health care bill while his colleague recovered.

Now, with the announcement from Moran and Lee, even if McCain were to return to Washington, McConnell would be unable to move his legislation to the Senate floor.

McConnell had hoped that Lee -- who had opposed the first version of the Senate bill -- would be won over by the addition of an amendment spearheaded by Sen. Ted Cruz . The provision would allow some insurers to offer cheaper and skimpier plans unregulated under Obamacare.

While it was enough to win Cruz's support, the amendment -- which Lee said was not exactly what he had asked for -- couldn't change Lee's mind. An aide to Lee said Monday night that throughout the process, "at most, he was undecided" -- a revealing comment about just how far away McConnell was from winning over some of his colleagues.

"In addition to not repealing all of the Obamacare taxes, it doesn't go far enough in lowering premiums for middle class families; nor does it create enough free space from the most costly Obamacare regulations," Lee said in a statement.

The fresh defections Monday night had Republican aides wondering whether the floodgates were about to open.

"Nobody wanted to be the third 'no,'" one GOP aide said. Now that there are four "no" senators, the number could grow very quickly and potentially open the door "to a whole stream of other 'no' votes," the source added.

In particular, senators hailing from Medicaid-expansion states have stubbornly remained holdouts as McConnell has searched for 50 "yes" votes.

Sens. Dean Heller of Nevada, Rob Portman of Ohio, Shelley Moore Capito of West Virginia and Lisa Murkowski of Alaska have all publicly said they were deeply uncomfortable with the steep cuts to Medicaid proposed in the Senate bill. In the most optimistic view, the new week-long delay brought on by McCain's absence was seen as offering these senators more time to negotiate and push for changes with leadership. But the Moran and Lee defections could very well shift the momentum and break a dam that has been ready to burst, aides said.

One Senate GOP aide with direct knowledge said Lee and Moran were likely to be first of many to publicly announce their opposition: "More senators are ready to jump. This wasn't done without that knowledge."