Collins, speaking on ABC's "This Week", said she had "very serious concerns" about the current bill and wanted to review the nonpartisan Congressional Budget Office's analysis of the proposal, which is expected to be released Monday, before deciding how she would vote.
Nonetheless, Heller's announcement underscores the scant margin of error Republican leaders must deal with.
In the narrowly divided Senate, defections from just three of the 52 Republican senators would doom the legislation. He said Medicaid will not be cut. The bill proposes phasing out federal funding to states that had been used to expand the program under the Obama administration.
Trump went on to acknowledge that not everyone would be happy with the GOP's replacement legislation for the Affordable Care Act.
"I can not support a piece of legislation that takes away insurance from tens of millions of Americans and hundreds of thousands of Nevadans", Heller said in a news conference held in his home state.More news: Mexico Eliminates Host Russia From Confederations Cup
More news: US Fed raises key rates for 2nd time this year
More news: Father of unified Germany Helmut Kohl dies
"If there's dissent on Medicaid, why don't we come back in six months and say, you know what, let's work with Democrats", Paul said.
"It's going to be a good bill", Trump said in a separate Fox News interview to air on Sunday. He spent much of his medical career working for Louisiana's charity hospital system, and he has said he has problems with the bill that won House passage in May and that was the building block for the Senate legislation unveiled Thursday (June 22). He added that Nevada "is one of the most improved states in the country" in expanding coverage.
At least two Republican senators on Sunday said that goal may prove too ambitious. It would be politically hard for Heller to take a different stance on the measure from the popular Sandoval. Rand Paul (R-Ky.), Ted Cruz (R-Texas), Ron Johnson (R-Wis.), Mike Lee (R-Utah) and Dean Heller (R-Nev.).
Underscoring the sensitivity of the bill, Sen.
On Thursday, four of the Senate's most conservative members said the new plan failed to rein in the federal government's role. "And unless it gets fixed, I would - look, I'm against it". They want to get some points.
Trump didn't indicate what types of changes may be in store, but affirmed that he had described a US House-passed bill as "mean". The Senate parliamentarian will make that decision.
Some Democrats are holding events this weekend to stand up against the bill.