Mr Trump has now acknowledged in an interview with Fox News that a lack of support from the four Republicans leaves the party's overhaul of former President Barack Obama's signature healthcare policy on a "very, very narrow path" to victory.
Heller made his announcement at a press conference where he was joined by Nevada Gov. Brian Sandoval (R), who previously has been critical of the GOP's efforts to eliminate the expansion as part of their Affordable Care Act repeal.
McConnell wants to push the package through the Senate next week, and will succeed if he can limit defections to two of the chamber's 52 Republicans. But a defeat would be a bitter and damaging blow to Trump and his party.
But company officials warned earlier this month premiums could jump an additional 20 percent if the Trump administration and Congress end "cost-sharing" payments created to bring down costs for more than 1 million Floridians.
On Saturday in Great Falls, Tester is holding a town hall to discuss the health care bill.
Molina Healthcare Inc, which has more than 1 million customers in Obamacare plans, said in a statement that dropping the individual mandate with no replacement provision will lead healthy people to forgo coverage and thus drive up premium rates. The big takeaways: The new bill will negatively affect key demographics, like Americans with substance use disorders, women, seniors and people with mental illness.
Heller is the fifth GOP senator to declare his opposition.
In an interview with Fox News Channel, Trump was asked about the four conservatives opposing the bill.
Republican Senator Dean Heller of Nevada just knifed TrumpCare, and it may not recover.
"Because, to be honest, the only way anything ever works here in Washington is when regular people stand up and demand something change", Sen.
Another incentive to maintain coverage would be to restrict eligibility for tax credits among people who let their coverage lapse.
McConnell, eager to approve the legislation next week, indicated he was open to changes before it reaches the Senate floor, but he said it was time to act.
Senator Bill Cassidy, who is still studying the proposal and has not yet decided how he will vote, said in several television interviews it was a good beginning.
The Senate bill's real-world financial impact is not yet known, but the nonpartisan Congressional Budget Office is expected to provide an estimate early next week. First, it eventually would end the Affordable Care Act - or Obamacare - expansion of Medicaid, through which 150,000 low-income Iowans have gained coverage.
The Senate plan would continue cost-sharing payments through 2019, then start offering less generous subsidies in 2020.
Medicaid covers 4 million people in Florida, including about half the childbirths and 70 percent of seniors in nursing homes and 41 percent of Palm Beach County's children.
Another possibility would be to limit plan choices for people who've had coverage lapses, allowing only catastrophic coverage or plans that cover a lower share of medical costs.