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WASHINGTON — President Donald Trump said Tuesday he would let Obamacare "fail" in the aftermath of his party's botched efforts to repeal and replace the Affordable Care Act.

"I think we're probably in that position where we'll let Obamacare fail," Trump said at the White House. "We're not going to own it. I'm not going to own it. I can tell you, the Republicans are not going to own it."

Once Obamacare collapses, Trump said Democrats would join Republicans so Congress would be able to “come up with new plan, really good for people.”

As for the GOP's recent failed efforts at an overhaul, White House Deputy Press Secretary Sarah Huckabee Sanders said the White House is taking responsibility "in terms of pushing new legislation through, but not for the failures of legislation that happened before the president got into office."

Democrats passed Obamacare, "creating the mess we're in," with their unwillingness to "work with Republicans in any capacity" on healthcare reform, Sanders reasoned.

The health care push withered after several Republicans — in a GOP-controlled Congress — refused to fall in line and vote for the bill.

Trump wouldn't go so far as to call Republicans who opposed the Senate repeal and replace efforts "disloyal," but he did say he was "very surprised" when two GOP senators yanked their support for the health care bill on Monday night, effectively killing it.

"The way I look at it is in (2018), we're going to have to get some more people elected...that are Republican," Trump said.

The president repeatedly said he was "very disappointed" with the health care defeat during a brief media availability with reporters Tuesday. "I am disappointed because for so many years I've been hearing repeal, replace," he said.

But Trump signaled that he remains ready to act, telling reporters that he's sitting in the Oval Office, "pen in hand, waiting to sign something."

Pointing the finger at Democrats was no new tactic for the president, who lashed out at "all of the Democrats and a few Republicans" earlier Tuesday morning. "We will return!" he promised in a tweet after the legislation was effectively killed.

“As I have always said, let ObamaCare fail and then come together and do a great healthcare plan. Stay tuned!” Trump tweeted.

“We were let down by all of the Democrats and a few Republicans. Most Republicans were loyal, terrific & worked really hard. We will return!” Trump wrote.

"With only a very small majority, the Republicans in the House & Senate need more victories next year since Dems totally obstruct, no votes!" he added.

Vice President Mike Pence echoed the president's tweets Tuesday morning during remarks at the National Retail Federation summit, issuing a stern warning to Congress to "step up" while declaring "inaction is not an option."

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"Congress needs to do their job, and Congress needs to do their job now," Pence said, urging Congress to move forward with a straight repeal of Obamacare — something they already voted to do in 2015.

"And as the president said with his inexhaustible optimism and determination, stay tuned. We will return," Pence added.

White House vows of a health care comeback began the morning after two more Republican senators said they would not support their party’s bill, leaving the GOP short of a majority and forcing Senate Majority Leader Mitch McConnell, R-Ky., to pull the plug on the measure.

Sens. Jerry Moran of Kansas and Mike Lee of Utah set the chain of events in motion Monday night in a surprise move when they announced on Twitter that they both would oppose the current bill, which was released just last week.

As I have always said, let ObamaCare fail and then come together and do a great healthcare plan. Stay tuned! — Donald J. Trump (@realDonaldTrump) July 18, 2017

We were let down by all of the Democrats and a few Republicans. Most Republicans were loyal, terrific & worked really hard. We will return! — Donald J. Trump (@realDonaldTrump) July 18, 2017

With only a very small majority, the Republicans in the House & Senate need more victories next year since Dems totally obstruct, no votes! — Donald J. Trump (@realDonaldTrump) July 18, 2017

Moran and Lee followed two other Republican senators who had already said they wouldn't back the plan: Rand Paul of Kentucky and Susan Collins of Maine.

With Senate Democrats united against the bill, the Senate Republicans could afford to lose only two of their own members support for the proposal.

My colleague @JerryMoran and I will not support the MTP to this version of BCRA #HealthcareBill — Mike Lee (@SenMikeLee) July 18, 2017

A senior administration official told NBC News on Tuesday that the White House wasn’t given a heads up before Lee and Moran announced they were pulling their support for the bill.

Moran and Lee tweeted their opposition just after Trump was finishing dinner at the White House with Republican lawmakers whom he thought could help him get the bill across the finish line.

Sen. James Lankford, R-Okla., who was at the dinner Monday night, said on Fox News Channel Tuesday morning that he and his fellow attendees also “did not know at that time” that their colleagues Moran and Lee were coming out against the measure. Moran and Lee were not at the dinner.

In another tweet Tuesday morning, Trump repeated his desire to see Senate Majority Leader Mitch McConnell change Senate rules to allow legislation to advance with just a simple majority vote, instead of the 60-vote, filibuster-proof majority currently required.

"The Senate must go to a 51 vote majority instead of current 60 votes. Even parts of full Repeal need 60. 8 Dems control Senate. Crazy!" the president tweeted.

The health care bill that didn't advance in the Senate Monday night, however, only needed 51 votes to pass, because it was being considered under a budget reconciliation process. That process would have allowed the bill to be pushed through with just a simple majority.

McConnell and other Republican senators have said previously they would not favor lowering the threshold for legislative votes. Republicans did change Senate rules to eliminate the filibuster for Supreme Court nominees earlier this year so they could approve Trump's nominee, Neil Gorsuch, along party lines.

The Senate must go to a 51 vote majority instead of current 60 votes. Even parts of full Repeal need 60. 8 Dems control Senate. Crazy! — Donald J. Trump (@realDonaldTrump) July 18, 2017

Meanwhile, a senior administration official admitted Tuesday that Trump had known the Senate health care bill was in “perilous” condition by Monday evening, adding that the White House had been floating a new plan — to repeal Obamacare now and replace it later — for quite some time.

On Monday night, McConnell, after acknowledging he didn’t have the votes for the measure after Lee and Moran bailed out, echoed that message, saying the Senate would instead vote on a full repeal of Obamacare, with two years before the repeal goes into effect to allow time to create a new system.

That new plan faces difficult odds. Many moderate Republican senators have already come out against repeal without an immediate replacement.

Trump quickly and publicly threw his support behind the new strategy, tweeting late Monday that “Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate.”

“Dems will join in!” he added in the tweet.

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

The setbacks Monday night were just the latest in a long line of roadblocks the GOP proposal has encountered since it was unveiled more than a month ago.

The first version of the bill fell short of the support needed when at least 10 Republican senators came out against it, forcing McConnell back to the drawing board to try to win the backing of additional moderate and conservative Republicans who had opposed the measure for different reasons.

But the fight isn't over, Sanders told reporters.

"This is not a game-over situation," she said, promising that the administration would continue to push for Republicans to make good on long-repeated vows to repeal and replace Obamacare.

Meanwhile, despite the latest health care defeat, some in the White House are vowing to forge ahead on another presidential priority: tax reform.

One senior administration source tells NBC News the plan is "going forward at full speed."

Trump's spirit dampened by disappointment over health care wasn't diminished when it came to other items on his agenda. He promised a "win" on taxes and infrastructure, two key legislative items the administration has said they'll prioritize this year.

The official said the bill's overall architecture would be in place by August recess, with full details and language when Congress returns in September followed by a full court legislative press until November. Congressional sources confirm this timeline, but say the biggest question is how specific they want to get ahead of the August recess.

Congressional leaders, including McConnell and House Speaker Paul Ryan, have been meeting regularly with Treasury Secretary Steven Mnuchin and National Economic Council Director Gary Cohn but the group has several outstanding issues — such as how to pay for corporate tax cuts — left to address.

Kristen Welker and Ali Vitali reported from Washington and Adam Edelman reported from New York.