When Judge Neil Gorsuch sat down for the first day of his Senate confirmation hearing on Monday, Democrats were fuming.

Not because of Gorsuch's political leanings, or the decisions he's made as an appellate judge on the U.S. Court of Appeals for the 10th Circuit.

They were mad because of Merrick Garland.

Garland, as you may remember, was President Barack Obama's nominee for the Supreme Court. Obama made his nomination formal a little over a year ago, on March 16, 2016. But Senate Majority Leader Mitch McConnell (R-Ky.) had already signaled he wouldn't even give Garland a hearing. He never did, and Democrats, furious with the departure from Senate norms, haven't forgotten.

Sen. Dianne Feinstein (D-Calif.) criticized Republicans who never took up the nomination of judge Merrick Garland, during a confirmation hearing for Supreme Court nominee judge Neil Gorsuch, on March 20 at the Capitol. (Reuters)

Now, Democrats say the last year amounts to a Republican attempt to pack the courts with politically conservative appointees. Democrats feel like Republicans spent more than a year stonewalling the rightful heir to Justice Antonin Scalia's seat. Garland's wait for a Senate hearing — one that never came — was the longest wait in U.S. Supreme Court history.

"This is a stolen seat. This is the first time a Senate majority has stolen a seat," Sen. Jeff Merkley (D-Ore.) told Politico in January.

The first Democrat to speak, Sen. Dianne Feinstein (Calif.), the ranking member of the Judiciary Committee, said she is "deeply disappointed" that Garland never got a hearing.

Then, Sen. Richard J. Durbin (D-Ill.) took it several steps farther.

"Your nomination is part of a Republican strategy to capture our judicial branch of government," Durbin told Gorsuch sternly. "That is why the Senate Republicans kept this Supreme Court seat vacant for more than a year, and why they left 30 judicial nominees who had received bipartisan approval of this committee to die on the Senate calendar as President Obama left office."

Sen. Richard J. Durbin (D-Ill.) said Republicans want to confirm Judge Neil Gorsuch to the Supreme Court as part of a "strategy to capture our judicial branch," during Gorsuch's Senate confirmation hearing on March 20 at the Capitol. (Reuters)

It's no secret that both sides want to pick justices they believe would rule in favor of the issues they care about. But to accuse Republicans so bluntly of trying to “capture our judicial branch of government” is pretty remarkable. The courts are supposed to be above politics — a point Gorsuch himself stressed repeatedly during his opening statement later Monday. Yet those assurances likely fell on deaf ears.

Judge Garland may not have made it very far in the Senate confirmation process. But his nomination, and Republicans' decision to not hold a hearing for him, could forever change the way Supreme Court nominees are chosen.

Senate Republicans hold a 52-48 advantage right now, and Democrats could try to filibuster Gorsuch's nomination. (Senate Minority Leader Charles E. Schumer of New York has already signaled that Gorsuch will need 60 votes to be confirmed.) It would be just the second time in modern history that a Supreme Court nominee has been filibustered. The more partisan his confirmation hearing gets, and the more the battle lines are drawn, the harder it could be for the GOP to round up the eight votes they would then need.