It’s no surprise President Donald Trump is quickly trying to fill the nearly 130 vacancies left on the federal courts by his predecessor. With a Republican majority in the Senate and a Republican in the White House, people may expect Trump’s nominees to sail through. But many people don’t know Senate Democrats can bring nominations to a standstill with a little-known practice called “blue slips.”

The president and the Senate share responsibility for placing judges on the federal courts. The president selects nominees, and the Senate evaluates them and votes in favor or against confirmation. The Senate Judiciary Committee handles the initial evaluation once the White House sends a nominee to the Senate.

Since 1917, however, the committee has asked senators from a nominee’s home state for their opinion — to be written on a blue slip of paper — before holding a hearing or further evaluating the nominee. This practice recognizes that home-state senators may be more familiar with a nominee and have better insights into his or her suitability for a judgeship.

Except for a brief period in the 1960s and ‘70s, a negative blue slip has not been treated like a veto on a nominee. But senators have been able to use the threat of a negative blue slip to persuade the president to select preferred nominees.

During the Obama administration, for example, Georgia Sens. Johnny Isakson and Saxby Chambliss, both Republicans, struck a deal with the president in which they agreed to return positive blue slips on seven nominees in exchange for Obama nominating one individual they supported. Not surprisingly, their nominee of choice was ultimately not confirmed by the Democrat-controlled Senate.

So far, it does not seem that Senate Democrats have been able to truly influence Trump’s selection of judicial nominees. He’s selected a slate of solid, conservative nominees with impressive backgrounds.

However, Sen. Al Franken, D-Minn., has complained that Trump sought input from conservative organizations such as the Federalist Society rather than him in selecting Minnesota Supreme Court Justice David Stras for a vacancy on the Eighth Circuit, the federal appeals court that covers Minnesota. There are also suggestions that Michigan Sens. Debbie Stabenow and Gary Peters, both Democrats, may try to hold up the nomination of Michigan Supreme Court Justice Joan Larsen to the Sixth Circuit Court of Appeals. Stras and Larsen have both been identified by Trump as possible Supreme Court nominees, so opposition to them for their current appointments will likely be fierce.

The blue slip, however, is not a permanent rule. In fact, it’s not even a formal Senate rule. It’s simply a practice adopted by the Senate Judiciary Committee that has changed many times over the years. Consequently, current chairman, Sen. Charles Grassley, R-Iowa, has several options for ensuring Democrats such as Franken, Stabenow, Peters and others don’t hold up qualified nominees.

For one, the committee could give more weight to blue slips for district court nominees than appeals court nominees. This is a logical distinction — district court judges only hear cases from the state where they sit, whereas appeals court judges are based in one state but hear cases from all the states within their circuit. Accordingly, home-state senators’ opinions are more relevant when it comes to district court nominees.

Another option is requiring senators to return their blue slips within a certain number of days, as many past chairmen have required. Or the committee could even acknowledge a negative blue slip but still proceed with holding a hearing and a vote on the nominee.

Finally, the committee could always do away with blue slips altogether, as Senate Democrats did with filibusters for lower court nominees in 2013. But Chairman Grassley would likely resist that option, no matter how much obstruction the Democrats put up; he knows that a future Republican minority in the Senate would benefit from having the blue-slip policy in place.

In addition to the confirmation of Neil Gorsuch to the Supreme Court, Trump has nominated 16 individuals to the federal courts. Yet the Senate has confirmed only one, appeals court judge Amul Thapar of Kentucky to the Sixth Circuit. 

The president has a long way to go to fill the more than 100 vacancies. Courts across the country lack good judges. This is no time for Senate Democrats to play obstructionist games.