With President Donald Trump’s second administration just weeks away, congressional Republicans are gearing up to execute on a wide-ranging legislative agenda touching on everything from taxes to immigration to fossil fuels. In a Monday interview with radio host Hugh Hewitt, Trump noted that his preference for doing so was “one big, beautiful bill,” but said he’d be open to two.

To accomplish that, Republicans intend to use a process known as budget reconciliation, which allows them to approve budget-related legislation with a simple majority in the Senate. Doing so enables them to bypass filibuster rules, which would otherwise require a bill to garner 60 votes to advance in the upper chamber. (In this case, with the Senate divided 53-47 in favor of Republicans, passing a bill through normal order would also require Democratic votes.)

There’s a catch for using this process, though, and it could become a major roadblock to parts of Trump’s agenda. As the name suggests, budget reconciliation is only intended to advance policies — such as spending and tax measures — that have a significant effect on the budget and not just an incidental one. Additionally, a restriction called the Byrd rule says that policies included in a budget reconciliation package aren’t supposed to affect Social Security or add to the deficit after 10 years. Provisions that don’t meet these standards typically get stripped out following an intensive review process, an outcome that has stymied both parties in the past.

Review of the legislation is done by congressional experts, including the Senate parliamentarian — a nonpartisan official who advises on the interpretation of congressional rules — to determine whether a bill meets these parameters. Lawmakers have the option to ignore the parliamentarian’s judgments, but it’s not common, and new Senate Majority Leader John Thune has already said

© Vox