Republicans, leading up to the contentious vote on U.S. Supreme Court nominee Neil Gorsuch, dubbed any Democratic filibuster of President Donald Trump’s nominee, “unprecedented.”

“Our Democratic colleagues have done something today that is unprecedented in the history of the Senate,” Kentucky Senate Majority Leader Mitch McConnell said on the Senate floor Thursday as Democrats filibustered the nomination. “Unfortunately, it has brought us to this point. We need to restore the norms and traditions of the Senate and get past this partisan filibuster.”

“Every excuse (Senate Democrats) have come up with to engage in this unprecedented filibuster is completely without merit,” Senate Majority Whip John Cornyn of Texas said Wednesday on the Senate floor.

Get Breaking News Delivered to Your Inbox

But the filibuster of a Supreme Court nominee — although very rare — isn’t entirely unprecedented, according to legal scholars and congressional records. Democrats’ short-lived filibuster of Gorsuch on Thursday — Senate Republicans almost immediately opted for a “nuclear option” to change Senate rules and end the filibuster — was not the first Senate filibuster of a Supreme Court nominee.

The only commonly recognized filibuster of a Supreme Court nominee on record occurred in 1968, when the Senate filibustered Abe Fortas, then-President Lyndon Johnson’s pick for chief justice, legal scholars told CBS News.

“Although there has not been a formal filibuster of a Supreme Court justice before, Republican Senator Strom Thurmond essentially did this in 1968 to block Justice Abe Fortas’s confirmation as Chief Justice,” Erwin Chemerinsky, dean of the University of California’s Irvine School of Law, told CBS News.

Fortas’ situation did differ some from Gorsuch’s. Fortas was already on the Supreme Court as an associate justice. Also unlike Gorsuch, opposition to Fortas was based on ethical grounds — he didn’t disclose $15,000 he received in speaking fees from a university. Differing from Gorsuch, in Fortas’ case, Republicans and Democrats alike pushed the filibuster.

That may be why some Republicans began calling a Gorsuch filibuster an unprecedented partisan filibuster, instead of an unprecedented filibuster.

The Fortas filibuster worked, as his supporters were unable to obtain enough votes to end it, and Johnson was ultimately pressured to withdraw the nomination.

The Senate has invoked cloture — an attempt to end debate on a nominee — four times in history, according to a report from the Congressional Research Service. In addition to the attempt with Fortas, the Senate invoked cloture during the nomination of former Justice William R. Rehnquist twice — once in 1971 and once in 1986 — and during the nomination of Justice Samuel Alito in 2006. The latter two attempts were successful. In 1971, the Senate failed to invoke cloture on Rehnquist but went on to approve him as associate justice anyway. Technically, some scholars say, those were also filibusters, although they aren’t typically considered as such.

Senate Republicans attempted to invoke cloture with Gorsuch Thursday and failed, so they pursued a change in Senate rules, or “nuclear option,” through which McConnell was able to end debate on Gorsuch and pave the way for Republicans to require only 51 votes instead of 60 to approve Gorsuch.

Kent Greenfield, law professor at Boston College Law School, said the Senate’s use of such a “nuclear” option to change the Senate rules and push a Supreme Court pick towards nomination is what’s unprecedented.

“This is the first time,” Greenfield told CBS News.

Chemerinsky also dubbed the elimination of filibustering for Supreme Court picks “unprecedented.”

But the “nuclear option” is built upon Obama-era precedent. Democrats in 2013 used a simple majority to push through a number of Obama appointees, giving McConnell precedent to end debate on Gorsuch.

“In terms of prior precedent, the most relevant would be that the Senate, Democrats ended the filibuster for lower federal court nominees and other executive branch nominees in 2013,” Paul Collins, Jr., professor and director of legal studies for the department of political science at the University of Massachusetts, Amherst, told CBS News.

Republicans have a point in claiming a simple majority vote is a return to how the Senate used to run.

Generally and historically, the Senate has voted on Supreme Court picks with an up-or-down, simple-majority vote, but the “major exception” to that was the Republican-led Senate’s refusal to hold a vote on Merrick Garland last year, Chemerinsky said.

The Senate is expected to take up a vote and approve Gorsuch with a simple majority Friday.