The results underscore the massive partisan divide on the executive branch powers that President Barack Obama wielded so assertively during his second term.

“This should be a huge lesson to any future president, that if you’re going to carry out massive regulations that don’t have the support of the American people or the American Congress, then perhaps you shouldn’t be doing it in the first place,” said Sen. Cory Gardner (R-Colo.), who called the outcome “a success for the American people.” He estimated that Congress’ nullification of the rules will save companies tens of billions of dollars in compliance costs.

Sen. John McCain (R-Ariz.) portrayed Republicans’ enthusiastic use of the review act as a deserved comeuppance for Obama. “I think it was bred by the fact that we had a president who said, ‘I’ve got a pen and I’ve got a phone,’ saying, ‘I’m disregarding Congress,’” he said.

But Democratic Sen. Brian Schatz of Hawaii had a warning for Republicans: Someday, his party will retake power in Washington.

“Now that this tool has been exercised, it’s available to everybody, and we’ll use it too,” Schatz said. He added: “As long as the statute’s available to us, then we’d be crazy not to utilize it for our purposes as well.”

In fact, though, Congress has successfully used the act only once before, to kill a Clinton-era ergonomics regulation in 2001. GOP attempts to use the review act during Obama’s presidency either failed to make it through Congress or died in presidential vetoes.

Republicans’ control of both Congress and the White House allowed them to dust off the 1996 law, which allows the rule-killing resolutions to pass by simple majority votes in both chambers. The regulations they killed included limits on stream pollution by coal companies, restrictions on broadband providers’ reselling of customer data, protections for Planned Parenthood’s state funding, and an anti-corruption rule requiring energy companies to disclose their payments to foreign governments.

Under the act, lawmakers can use the tool to bypass Senate filibusters within 60 legislative days after a rule takes effect, a period that is due to expire on Thursday for Obama’s final regulations. Lawmakers could have tried to block any of the dozens of significant Obama-era regulations that took effect after June 2016, but their capacity was limited by other priorities on Congress’ calendar, such as confirming Trump’s Cabinet nominees and dealing with Obamacare.

In addition, the Obama administration made sure to finish most of its blockbuster regulations long before they would become vulnerable to the congressional attack.

That meant the repeals were as much about symbolically attacking Obama as they were about the substance of each targeted rule, said Philip Wallach, a senior fellow at the Brookings Institution.

“My understanding is the collectivity of these rules kind of seems like largely a rebuke of the Obama administration in a pretty general sense, rather than necessarily showing that Congress thought very hard about exactly what was at stake with each of these rules,” he said.

Still, Republicans say they’re satisfied with what they accomplished.

“I think we’ve taken maximum opportunity to look at things the country lived without for 228 years, and the Obama administration lived without for at least 7 1/2,” Sen. Roy Blunt (R-Mo.) said. “That kind of late rulemaking probably doesn’t deserve to be permanent if you can do anything about it. We did.”

Democrats generally expressed dismay over the rules the GOP axed, although many said bigger battles were being waged elsewhere. “They did some damage, but in the scheme of things I don’t think you look at those CRAs and say that President Obama’s legacy is undermined,” Schatz said.

However, the GOP’s frequent use of the review act this year could raise new legal questions down the road. That’s because the law doesn’t just allow Congress to block the targeted regulations — it also prohibits agencies from ever issuing a rule that is “substantially the same.”

That prohibition has never been tested by the courts. (The Labor Department never tried to revisit the ergonomics rule that Congress struck down in 2001.) But it was one reason Democratic leaders avoided using the review act in 2009 to attack the George W. Bush administration’s midnight regulations — it could have made it harder for Obama’s agencies to strengthen the same rules later.

Some of the rules Republicans squashed this year could face similar questions someday. For example, six Senate Republicans who voted to kill the Securities and Exchange Commission’s anti-corruption rule later said they hope the SEC will issue a new version with some key changes. But it’s unclear whether any alterations would get around the review act’s similarity test.

Now that the clock is expiring, the Trump administration is using other, slower methods to try to repeal or weaken Obama-era rules across the government. It could take years for those efforts to yield results and survive the inevitable court challenges, including the EPA’s efforts to repeal Obama’s power plant climate rule, toughened smog standards and a nationwide regulation protecting wetlands and waterways.

The Congressional Review Act was a healthy start, Republican lawmakers said.

“I think it’s been very helpful, but we still have a couple thousand more [rules] that Obama issued over the last eight years,” McCain said. “We’re still going to have to work on some of that.”