The threat to do away with Obamacare is once again on the rise nearly 10 years after it was passed, as a major challenge to the health care law got a sympathetic-sounding hearing in a federal appeals court this week.

If the case does ultimately reach the Supreme Court , and five justices agree to strike down the Affordable Care Act , experts say it would upend the U.S. health care system and strip health insurance from an estimated 20 million people. Many millions more would lose crucial protections they might need in case of catastrophic medical issues including coverage for those with preexisting conditions.

Republicans in the U.S. Senate dont appear to be sweating the likelihood of such a scenario, however. Some are pinning their hopes on the courts to reject the challenge, which is backed by the Trump administration, on the grounds that it isnt serious and is legally moot.

I actually dont think the courts are eventually ever going to strike it down, Sen. Lamar Alexander (R-Tenn.) said Wednesday. He called the case, which was argued before an appeals court in New Orleans on Tuesday, pretty far-fetched.

Sen. Susan Collins (R-Maine), a supporter of the law who helped save it in 2017 when Republicans in Congress attempted to repeal it, agreed.

Its my hope and belief that the Supreme Court wont strike the law down, Collins said.

Still, the latest challenge to the law has advanced in the courts despite widespread derision from legal experts , including conservatives who helped construct and argue previous challenges to the ACA.

It stands a good chance of being taken up by the Supreme Court next year, smack dab in the middle of the 2020 presidential election, creating another headache for the GOP.

Republicans have tried over and over again to coalesce around a cheaper and less government-focused replacement for Obamacare, and theyve failed every time. Cobbling together a plan that preserves some of the most popular parts of the law such as its guarantees of coverage for people with preexisting conditions, expanded Medicaid coverage, and provisions allowing young people to remain on their parents policy until the age of 26 without a mechanism like Obamacare is extremely difficult, and maybe even impossible, a fact that even some Republicans acknowledge.

Maybe this is the thing that forces Republicans to come up with a consensus idea of what to do, but weve been down this path numerous times without any success on an agreement, Sen. Jerry Moran (R-Kan.) said Wednesday when asked about the latest legal challenge to the law.

Senate Majority Leader Mitch McConnell (R-Ky.) has made clear that he has no plans to take up broad health care legislation until after the 2020 election. (He said so after Trump, seemingly out of nowhere, pledged earlier this year that Republicans will become known as the party of health care.)

But in a sign of how far the politics surrounding Obamacare have shifted, McConnell vowed this week to restore coverage for people with preexisting conditions should the Supreme Court uphold the challenge to the law.

We would act quickly, on a bipartisan basis, McConnell said at a news conference on Tuesday.

Sen. Thom Tillis (R-N.C.) introduced legislation earlier this year aiming to do just that. Republicans are pointing to the bill as evidence of their good faith commitment to those with preexisting conditions. But while it does prohibit insurers from denying applicants based on pre-existing conditions, experts say Tillis bill leaves out several other protections found in the ACA, such as its ban on annual or lifetime limits on benefits, or its provision prohibiting insurers from charging women more than men.

Some Republicans also find it lacking.

Its my understanding it does not cover essential health benefits and I think those are important parts of the ACA as well, such as mental health, substance abuse, maternity care, etc. But it is a good start, Collins told reporters when asked about Tillis bill on Tuesday.