Despite the fact that President Trump and Congress can't agree on a health-care plan, a U.S.-Mexico border wall and the budget, Trump has managed to sign legislation undoing more than a dozen of former president Barack Obama's rules on education, the environment, health care and labor.

Trump has undone so many regulations that, besides getting a Supreme Court nominee on the court, unraveling Obama rules on guns, coal dumping, Internet privacy and more is probably the president's (and congressional Republicans') biggest 100-day accomplishment.

But Republicans' days of being able to systematically repeal Obama rules with a majority-rule vote in Congress and a flick of Trump's pen are numbered. And that's bad news for a party that hasn't figured out how to pass legislation without relying on an obscure, little-used law to get things done.

Here's a look at the Congressional Review Act that Congress and Trump have been using to score easy legislative victories and why they'll soon no longer be able to use it.

What the Congressional Review Act is and does

President Barack Obama speaks to Congress in 2015. (Astrid Riecken/European Pressphoto Agency)

The law allows Congress to repeal a federal regulation with a simple majority (read: no need to involve Democrats), so long as that federal rule was implemented no more than 60 legislative days earlier.

To understand why Congress would need such a law, we have to understand the relationship between Congress and the federal agencies: Congress has the power to create laws, and the executive branch figures out how to implement those laws in the form of regulations or rules.

But for most of the 20th century, Congress was micromanaging how agencies implemented these rules by vetoing stuff it didn't like. In 1983, the Supreme Court said that was an unconstitutional violation of the separation of powers.

Then-House Speaker Newt Gingrich (Ga.) and his fellow congressional Republicans found a way to give Congress the ability to veto regulations again, but this time, repealing a federal rule would need the president's signature (there's your check and balance, Supreme Court). The Congressional Review Act passed in 1996.

Why the clock is ticking on being able to use it

Since Congress has had this power to undo federal regulations, the Congressional Review Act has been used only once (Republicans in Congress and President George W. Bush undid a Bill Clinton workplace ergonomic program in a day).

The law has never been used before the way Republicans are using it — to undo a dozen rules the previous administration signed.

That's because this law is highly dependent on a window in time. Presidents won't sign legislation undoing their own rules. So the Congressional Review Act is pretty much helpful only in the very short time when there's a transition of power from one party to another — i.e., when Congress and the president are united in opposition to a rule that was implemented just 60 legislative days ago.

We're still in that 60-day window, but barely. Obama left office 95 days ago, but Congress has been in session for about 50 days this year. By our calculations, they've got about a month of real-people time left (10 congressional days) to undo rules the Obama administration implemented on its way out the door.

What rules have been undone so far

There are about 50 more Obama-era regulations Congress could have quickly undone, including limits on bird hunting, protections for nursing patients and fuel standards for trucks. Trump has signed into law 13, and 21 more are pending.

President Trump signed four bills removing various federal regulations on March 27 at the White House. (The Washington Post)

Here are the rules Republicans have undone:

  • They've lifted rules preventing coal-mining operations from dumping their waste into streams.
  • They've ended a rule that prevented states from cutting off funding to Planned Parenthood and other abortion providers. (Now states can legally cut off such funding; Kentucky already has.)
  • They've eliminated new training programs for K-12 teachers.
  • They've lifted a rule preventing people with mental health problems from buying guns.
  • They've lifted a rule that prevented federal land hunting of mother bears and cubs, and wolves and pups, as part of predator control. (Now the game board can use those predator control methods. Environmental groups are suing the Trump administration over this rule, alleging that the Congressional Review Act violates the separation of powers. It remains to be seen how far they'll get.)
  • They undid a rule requiring large federal contractors to disclose and fix serious safety and labor law violations before they get a contract.
  • And they undid a rule that had prevented service providers, including Verizon, AT&T and Comcast, from collecting users' browsing habits and other data to sell to marketers. (Now these Internet service providers can do that.)

In a time when Trump and Republicans have been unable to agree on the mechanics for repealing the Affordable Care Act or passing a spending bill, this rule was pretty helpful to allow them to show forward movement to a base that despises federal regulations. Unfortunately for Republicans, time is running out to use it.