An influential Republican lawmaker who was chairman of one of the House committees that drafted the GOP proposal to repeal and replace ObamaCare dealt the Trump administration a blow Tuesday when he said he could not support the new healthcare legislation being drafted.

“I cannot support the bill with this provision in it,” Rep. Fred Upton of Michigan told a radio station. Upton believes the bill would undermine protections the Affordable Care Act – or ObamaCare – gives people with pre-existing conditions.

Upton’s defection comes as House Speaker Paul Ryan tries once more to make good on campaign promises to repeal and replace former President Barack Obama’s signature health care overhaul.

Republican leaders are still short of the 216 votes they need to win. President Trump and Ryan are trying to resurrect a revised version of the bill Ryan was forced to pull in March when it became clear they didn’t have the votes needed to secure a win.

Upton told The Associated Press that the bill's treatment of people with pre-existing illnesses "does not fit" with comments Trump made in an interview last weekend. The president said "Pre-existing conditions are in the bill."

"Can there be a fix? Maybe, but it is not part of the equation before us," Upton said.

Upton pointedly noted that the bill's language on pre-existing conditions was backed by the House Freedom Caucus, most of whose deeply conservative members now support the legislation.

In a radio interview earlier Tuesday on "WHTC Morning News" in Holland, Michigan, Upton made similar remarks and said "a good number of us have raised real red flag concerns" about the bill to leaders.

The issue seeped into popular culture late Monday when late night talk show host Jimmy Kimmel delivered an emotional 13-minute monologue describing the recent birth of his son, who had heart disease that required immediate surgery that proved successful. Kimmel said before Obama's law took effect, many such infants could die because they'd be uninsured because of their pre-existing condition.

"If your baby is going to die and it doesn't have to, it shouldn't matter how much money you make," Kimmel said. He added, "We need to make sure that the people who are supposed to represent us, people who are meeting about this right now in Washington, understand that very clearly."

Kimmel's remarks inspired Obama to weigh in on Twitter.

"Well said, Jimmy. That's exactly why we fought so hard for the ACA, and why we need to protect it for kids like Billy. And congratulations!" he wrote, referencing his Affordable Care Act.

Trump briefly referenced the health care measure with remarks during a White House ceremony honoring the Air Force's football team, asking lawmakers in the audience how the bill was faring.

"I think it's time now, right?" he said. "They know it's time."

A senior Trump adviser said the White House counts them as being five votes short on the bill, a number that could drop to zero or grow to 15. The official signaled that the White House would pin the blame for falling short on GOP leaders, saying "Let's see if the Hill can deliver."

Ryan said leaders are "making very good progress" in winning support.

The legislation would lose if 22 Republicans vote no, assuming all Democrats vote against it.

Since last week, 21 Republicans have said they oppose the legislation, according to a count by The Associated Press. At least 11 others have said they are undecided. Those numbers are subject to change as the White House and House leaders pressure rank-and-file lawmakers to back the legislation.

Under Obama's 2010 law, insurers may not charge seriously ill customers higher premiums than healthy ones.

The latest revised GOP bill bars insurers from limiting access to coverage for people with pre-existing conditions.

But states can obtain federal waivers letting insurers raise premiums on people with pre-existing illnesses, though only if the customer has let their coverage lapse during the previous year. The state must also have a high-risk pool or another mechanism to help such people afford a policy.

Supporters of the GOP legislation say it protects people with pre-existing conditions and that the exclusion would affect only a small proportion of them.

Opponents say it diminishes their protections by letting insurers charge unaffordable prices. They also say high-risk pools have a mixed record of effectiveness, often because the government money provided to finance them proves inadequate.

The bill would let states get waivers to Obama's requirements that insurers cover specified services like hospitalization and preventive care, and would let them make premiums on older people more than five times higher than they charge younger ones.

The Associated Press contributed to this report.