(CNN) President Donald Trump on Friday called for repealing the Affordable Care Act immediately and replacing it later with another health care plan if Republican senators are unable to pass their bill.

"If Republican Senators are unable to pass what they are working on now, they should immediately REPEAL, and then REPLACE at a later date," tweeted Trump.

If Republican Senators are unable to pass what they are working on now, they should immediately REPEAL, and then REPLACE at a later date!

Trump's declaration -- which marks a political shift for him and could further imperil delicate negotiations on Capitol Hill -- came shortly after Sen. Ben Sasse, R-Nebraska, urged the President in a letter to repeal Obamacare now and replace later. The current Republican plan in Congress is to do both in one massive piece of legislation, though the Senate's bill has struggled to gain necessary GOP support.

"On July 10, if we don't have agreement on a combined repeal and replace plan, we should immediately vote again on H.R. 3762, the December 2015 ObamaCare repeal legislation that the Congress passed but President Obama vetoed," Sasse wrote in the letter . "We should include a year-long implementation delay to give comfort to Americans currently on ObamaCare that a replacement plan will be enacted before expiration."

A Senate aide told CNN that Sasse's team and the White House had been privately discussing getting the President to publicly support a straight repeal bill. Once the two sides became confident that Trump was interested, they drafted Sasse's letter and arranged for him to appear on Fox News Friday morning to call for such a plan.

Sasse quickly approved of Trump's tweet.

"Sounds great, Pres. @realDonaldTrump We are agreed. We need to break the logjam," he tweeted.

Trump's message Friday morning also marked a notable return to his efforts to push his agenda rather than distract from it, as he did on Thursday when he viciously and personally attacked MSNBC anchor Mika Brzezinski.

Trump was criticized heavily on both sides of the aisle for the outburst, with Sasse saying the tweets were "beneath the dignity" of his office.

A 'hand grenade' in negotiations?

White House deputy press secretary Sarah Huckabee Sanders said Trump "hasn't changed his thinking at all" on health care as she fielded a question on Trump's tweet this morning on the health care reform efforts.

"We're still fully committed to pushing though with the Senate at this point, but we're looking at every possible option of repealing and replacing Obamacare. We are focused on doing that," Sanders said.

Sanders also said she did not know where Trump got the idea for that plan, noting that "people have been talking about this for quite some time."

"I don't know where specifically it may have come from," she said.

But Trump's tweet appears to mark a new public stance for him regarding health care.

Days after being elected, he told CBS's Lesley Stahl on "60 Minutes": "It'll be repeal and replace. It will be essentially, simultaneously. It will be various segments, you understand, but will most likely be on the same day or the same week, but probably, the same day, could be the same hour."

Trump reiterated that position at a news conference as President-elect back in January.

"We're going to do it simultaneously," he said. "It'll be just fine. We're not going to have, like, a two-day period, and we're not going to have a two-year period where there's nothing. It will be repealed and replaced."

The President's tweet also could have the effect of further complicating health care negotiations. A GOP official close to leadership and supportive of the current repeal/replace effort told CNN: "Nothing like rolling a hand grenade into ongoing negotiations, eh?"

JUST WATCHED Psaki: Dems should negotiate healthcare with GOP Replay More Videos ... MUST WATCH Psaki: Dems should negotiate healthcare with GOP 06:20

The concern, the official outlined, is that this now gives conservatives a reason to go back to their corner. While they were hardly at the breakthrough point, there's no question conservatives, particularly Sen. Ted Cruz, had been working in good faith to get to a deal.

Now the concern is conservatives can just say they wanted the 2015 repeal bill all along, and because the President clearly supports that plan, talks on a sweeping replacement plan can be scrapped.

A GOP Senate aide noted Trump's initial opposition to a straight repeal bill.

"We did this dance six months ago," the aide said. "We've litigated repeal, delay, replace. Thoroughly. The President spoke against it. This all might be more helpful if we weren't in the late stages of negotiations."

Appearing on CNN's "New Day" on Friday, Rep. Adam Kinzinger, R-Illinois, also rejected the President's suggestion.

"I think it's repeal and replace," he told CNN's Chris Cuomo. "We can argue whether they like the system we're bringing them in or not, but simply a repeal, even with the sunset the year or two down the road -- the problem (is) we know how Washington works."

He explained: "Sometimes on deadlines we still don't get things done. You can't leave the American people out like this. This is how sequester happened, because we thought we could fix the problem and never did."

'Big surprise'

Earlier this year, Hill Republican leaders floated the idea of repealing Obamacare and providing a transition period during which Congress would write a new law. But many Republicans opposed that idea, and along with Trump calling for passing both simultaneously, the party shifted tactics.

One reason behind that shift is repealing Obamacare without an immediate replacement plan would likely cause massive destabilization to an insurance market already unnerved by Washington's efforts to address health care. Many insurers are asking for another round of steep rate increases for 2018, and others aren't even willing to return to the exchanges at all.

But some companies say the market is stabilizing, so they plan to stay in the game and charge only a little bit more next year.

The Affordable Care Act was troubled even before Trump took office, but the Republicans' quest to dismantle it has made things worse. Trump has caused confusion about whether he'll continue key components of the law. The two at the top of the list: the mandate that everyone have insurance and the cost-sharing subsidies for lower-income Americans.

JUST WATCHED McConnell threatens bipartisanship Replay More Videos ... MUST WATCH McConnell threatens bipartisanship 02:13

Polling shows repealing Obamacare outright was the least popular option as House Republicans began negotiating on health care. According to a March CNN/ORC survey , just 17% of Americans favored repealing parts of the bill as opportunities arose, regardless of whether a replacement was ready, including only 26% of Republicans.

Meanwhile, the future of the GOP health care efforts remains unclear. Senate Republican leaders scuttled plans for a vote on health care reform earlier this week as GOP leaders criticized the bill, but Trump was optimistic in his outlook Wednesday.

"We're going to have a big surprise," Trump said during a brief photo opportunity with reporters as he welcomed the World Series-winning Chicago Cubs at the White House. "We're going to have a great, great surprise."

Trump declined to say what the surprise would be, but his optimism contrasted significantly with the nine Republican senators publicly expressing their opposition to the bill the President is championing.

The White House can only afford to lose two of the 52 Republicans in the Senate to pass the legislation.