WASHINGTON - Two Republican senators signalled strong opposition Sunday to their party’s latest bid to overhaul Obamacare, dealing a potentially fatal blow to one President Donald Trump’s top legislative goals.

Senator Susan Collins of Maine said she cannot “envision a scenario” in which she would back the legislation, and Senator Rand Paul of Kentucky said he would support it only if a key provision changing the way health care funding works were dropped.

Their comments were more bad news for the White House, after US Senator John McCain announced Friday his opposition to the latest Republican effort to replace or at least revamp Obama’s signature health care law.

The deadline for passing the legislation is September 30, the end of the fiscal year.

Republicans hold 52 of the 100 seats in the Senate. In the event of a tie, Vice President Mike Pence could cast a vote to break it. So the Republicans could afford only two defections at most. And now there appear to be three, meaning the bill could likely be dead on arrival when it reaches the Senate.

Collins, speaking on CNN, laid out a number of complaints, including the bill’s impact on Medicaid — the health care program for the poor and people with disabilities — and on coverage for people with pre-existing conditions.

“It is very difficult for me to envision a scenario where I would end up voting for this bill,” Collins said. Paul objected to a key provision of the bill, under which Obamacare funding would be granted to states in blocs for them to decide how to spend, rather than be managed by the federal government.

“What it sets up is a perpetual food fight over the formula,” Paul told NBC. “What happens when Democrats win? They’re going to claw back that money from Republican states to give to Democrat states.”

The White House scrambled last week to win over Republicans skeptical of the so-called Graham-Cassidy bill, with Trump himself telephoning lawmakers and state governors seeking to tilt the scales in favor of the bill. And Trump made his position on Republican defectors clear on Friday, writing on Twitter that those who vote against Graham-Cassidy “will forever... be known as ‘the Republican who saved Obamacare.’”

While Republicans have pledged to repeal the Obama-era health care reforms, they have struggled to secure enough support to do so amid fears that proposed alternatives would dramatically increase the number of Americans without health insurance.