Tracking Trump's shifting stances on health care Trump has offered at least three different positions on undoing Obamacare.

 -- Congressional Republicans' last-ditch attempts to undo Obamacare have put a spotlight on President Donald Trump's shifting positions on how to achieve that long-held GOP goal.

After the Senate bill to overhaul health care collapsed early this week, Trump on Tuesday called for Republicans to "let Obamacare fail." But he had earlier pushed to simultaneously repeal and replace the Affordable Care Act and, alternatively, to just repeal it.

"I think the president's been clear that what he wants is repeal and replace," said White House Director of Legislative Affairs Marc Short at Wednesday's press briefing. "That's what he said during the transition, that's what he said ever since."

But Short conceded that, given the hurdles facing proposals to replace the health care law, the administration "should at least deliver on the promise to repeal."

Here is a look at Trump's shifting position on health care:

Repeal and replace

Trump's stated preference for repealing and replacing the Affordable Care Act traces its roots back to day one of his presidential campaign in June 2015, when he officially announced his bid for the Republican nomination at Trump Tower in New York.

"We have to repeal Obamacare ... and it can be replaced with something much better for everybody," said Trump. "Let it be for everybody. But much better and much less expensive for people and for the government. And we can do it."

The repeal-and-replace pledge became a central theme of the real estate mogul's campaign, regularly promised in stump speeches, in tweets and at major public appearances, such as his address to the Republican National Convention in July 2016.

"We will repeal and replace disastrous Obamacare," said Trump during his acceptance speech at the RNC.

A search in an ABC News archive of transcripts of 2016 campaign events found Trump using the words "repeal" and "replace" more than 50 times following the convention through Election Day, including repeated assurances that this would take place "immediately."

The vow to both repeal and replace continued after Trump took office as he promoted his agenda on social media.

During his first joint address to Congress in February, he asked lawmakers to follow through on the pledge.

"Tonight, I am also calling on this Congress to repeal and replace Obamacare," said the president.

Repeal only, then replace

After Sens. Mike Lee, R-Utah, and Jerry Moran, R-Kansas, simultaneously announced their opposition to the Senate health care bill Monday evening, Trump appeared willing to yield on his original pledge.

"Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate," he tweeted.

This idea -- to wipe out his predecessor's signature legislation and then pass its replacement at a later time -- was one Trump had expressed earlier. Less than three weeks prior, he tweeted that if Republican senators are "unable to pass what they are working on now" they should repeal first.

As far back as May 2016, Trump's campaign website included a page suggesting a possible strategy of repealing first, replacing later.

"On day one of the Trump Administration, we will ask Congress to immediately deliver a full repeal of Obamacare," reads an archive of the website.

The page does not follow by promising an immediate replacement, but says, "it is not enough to simply repeal this terrible legislation. We will work with Congress to make sure we have a series of reforms ready for implementation that follow free market principles and that will restore economic freedom and certainty to everyone in this country."

"Let Obamacare fail"

Only hours after his Monday-night tweet in support of repeal then replace, the president offered a different approach.

"As I have always said, let ObamaCare fail and then come together and do a great healthcare plan," he tweeted.

Trump doubled down on the approach when asked by reporters about the apparent failure of the attempt at a simple repeal.

"We'll just let Obamacare fail. 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,” he said.

It was not the first time Trump showed a willingness to allow the health care law to remain in place. When House Republicans' American Health Care Act was pulled from consideration ahead of an anticipated vote in March, the president expressed exasperation in remarks from the Oval Office.

"I've been saying for the last year and a half that the best thing we can do politically speaking is let Obamacare explode," said Trump, despite comments earlier in his presidency that allowing Obamacare to "blow itself off the map" was "the wrong thing to do for our citizens."

The House eventually passed its health care bill, after which Trump hosted House Republicans for a celebratory press conference from the Rose Garden.

ABC News' Devin Dwyer, Cheyenne Haslett and Karen Travers contributed to this report.