WASHINGTON ― If Republicans make good on their pledges to try and repeal Obamacare, incoming Senate Minority Leader Chuck Schumer (D-N.Y.) says it will only end in disaster for the GOP.

Republicans have voted dozens of times to repeal President Barack Obama’s Affordable Care Act, which has extended health insurance to some 20 million Americans since it passed.

Part of the problem for Republicans hoping to end Obama’s signature achievement is that key parts of it are immensely popular, such as allowing young adults to stay on their parents’ health plans until they’re 26, and ensuring that people with pre-existing conditions can get insurance.

Republicans, even in the fairly unspecific proposal they rolled out last summer, have said they would preserve some of those Obamacare reforms, although their plans don’t provide equivalent guarantees of coverage, and do not include specific figures about how much the federal government would spend to help people get insurance.

And therein lies the problem for the GOP.

“They’re going to find they have a tiger by the tail because of all the good things in ACA,” Schumer told The Huffington Post, pointing to the 20 million newly insured people, the pre-existing condition rules, the young adult provisions and other parts such as prohibitions against charging women more than men.

“It’s impossible for them to keep those — which they say they want to keep — without keeping the ACA,” Schumer said. “They’re going to be like the dog that caught the bus.”

Schumer likely has a point. Many of the parts of the Affordable Care Act that the GOP wants to dump are the cost controls and provisions that pay for the law. If the funding side of the law is eliminated, it becomes very difficult to sustain any of the reforms. Similarly, without a penalty that forces healthy people to pay for coverage, it’s hard to require insurers to cover people with pre-existing conditions.

House Ways and Means Committee Chairman Kevin Brady (R-Texas), who will have a key role in authoring repeal legislation since much of it concerns taxes, told HuffPost recently that the GOP does intend to keep the popular provisions.

He acknowledged that it’s costly, but like the GOP’s plan itself, he offered few details about how the popular items would be funded, beyond pointing to a theoretical increase in competition and a GOP proposal to cap existing tax breaks on some high-quality employer-based health plans.

“Since we’re doing away with all the taxes and mandates, unlocking that tax break and giving people freedom to use it to choose a plan that’s right for them is really the key to the Republican proposal,” Brady said.

Schumer thinks the reason there are so few specific numbers is that once real numbers are available, it will be obvious how much damage the Republican repeals will do to Americans.

“None of them have been able to come up with a plan that keeps all the parts that are popular without keeping ACA,” Schumer said. “They’re going to be so stuck. I look forward to them marching into that issue. They will regret the day they did it.”