The Georgia runoff results adding a majority in the Senate to the one Democrats already had in the House gave the party a fresh tool to reverse Trump administration policies.

Why it matters: The Congressional Review Act (CRA) empowers a majority in Congress to undo recent rules issued by federal agencies — including immigration restrictions, environmental rollbacks and labor regulations.

• The power can be used in tandem with executive orders from the White House. President-elect Biden told reporters Friday one of his first priorities will be to use his executive orders to "countermand" those issued by President Trump.

How it works: Any rule enacted in the last 60 working days of a Congress — in this case since Aug. 21 — can be reviewed by the next Congress, according to Daniel Pérez. He's studied the CRA as a senior policy analyst at George Washington University's Regulatory Studies Center.

• At least 1,354 rules would technically qualify for this review, according to the Federal Register.
• A targeted rule could be blocked with simple majority votes in both the House and Senate.
• A practical restraint comes from the mechanics: Congress can't start its review until the 15th working day after it's seated, and it only has 60 days to complete its work.
• In addition, each regulation must be debated and voted upon individually in each chamber. That's a potentially time-consuming process in the face of other pressing congressional business.

Flashback: Republicans made unprecedented use of the CRA at the start of the Trump administration. It had been successfully used only once before, but they blocked 16 Obama-era agency rules.

But, but, but: While it is one of the most efficient ways to undo agency regs, the CRA can be a blunt tool. Rules can't be modified — only rejected completely. And if rejected, a similar rule can't be issued.

• Some of Trump's biggest policies, such as those related to immigration, are already being challenged in the courts. Experts say it may be easier to simply let those legal fights play out.
• Rules also can be undone or amended through the full regulatory process, although that can take months.