Harry Reid, a Democrat from Nevada, is Senate minority leader.

We are entering uncharted waters in the history of the U.S. system of checks and balances, with potentially momentous consequences. Having gridlocked the Senate for years, Republicans now want to gridlock the Supreme Court with a campaign of partisan sabotage aimed at denying the president’s constitutional duty to pick nominees.

Republicans should not insult the American people’s intelligence by pretending there is historical precedent for what they are about to do. There is not.

The Senate has confirmed Supreme Court nominees both in election years and in the last year of a presidency — as recently as 1988, a presidential election year when a Democratic Senate confirmed President Ronald Reagan’s nomination of Justice Anthony M. Kennedy in the final year of his administration. My colleague and the chairman of the Judiciary Committee, Sen. Chuck Grassley (R-Iowa), was a member of the Judiciary Committee then and voted to confirm Kennedy. More recently, Sen. Grassley stated, “The reality is that the Senate has never stopped confirming judicial nominees during the last few months of a president’s term.” That is true. For his part, my counterpart, Senate Majority Leader Mitch McConnell (R-Ky.), on Saturday called for the American people to have a “voice” in this process. Their voice was heard loud and clear when they elected and reelected President Obama, twice handing him the constitutional power to nominate Supreme Court justices.

That is how our system works and has worked for more than 200 years. Until now, even through all the partisan battles of recent decades, the Senate’s constitutional duty to give a fair and timely hearing and a floor vote to the president’s Supreme Court nominees has remained inviolable. This Republican Senate would be the first in history to abdicate that vital duty.

Washington Post reporter Robert Barnes explains where the Supreme Court stands after the death of Justice Antonin Scalia and how the vacant seat will impact the presidential election. (Whitney Leaming/The Washington Post)

[Read more: If Republicans block Obama’s Supreme Court nominee, he wins anyway]

This constitutional duty has transcended partisan battles because it is essential to the basic functioning of our co-equal branches of government. By ignoring its constitutional mandate, the Senate would sabotage the highest court in the United States and aim a procedural missile at the foundation of our system of checks and balances.

The good news is that there is still time for heated rhetoric to yield to reasoned action. The Senate can get there if Republicans take a deep breath, put partisan politics aside and think this through, as Americans first and foremost. It is easy to get caught up in the partisan swirl of an election year, but I would urge my Republican colleagues to remember that the consequences of blocking any nominee, regardless of merits, would hang over their heads for the rest of their careers.

The rash statement that Sen. McConnell issued a few hours after Justice Antonin Scalia’s death was announced framed the precedent at stake in the broadest possible terms, arguing that, starting now, any president should be denied the right to fill a vacancy in a presidential election year. Not only is that principle absurd on its face, but if we set that precedent now, there is nothing to stop future Senates from sliding further down that slippery slope. It is a small and easily envisioned step to go from “no Supreme Court confirmations in this specific election year” to “no confirmations in any election year.” Our founders who envisioned a fair, bipartisan process must be rolling in their graves.

If we enshrine this precedent and declare a functioning Supreme Court optional, subordinate to the whim of the Senate majority, it is easy to envision a future where the Supreme Court is routinely crippled.

If my Republican colleagues proceed down this reckless path, they should know that this act alone will define their time in the majority. Thinking otherwise is fantasy. If Republicans proceed, they will ensure that this Republican majority is remembered as the most nakedly partisan, obstructionist and irresponsible majority in history. All other impressions will be instantly and irretrievably swept away.

My Republican Senate colleagues should know, too, that they will be unconditionally surrendering their party to hard-line presidential candidates Sen. Ted Cruz (R-Tex.) and Donald Trump. Behind closed doors, many of my colleagues complain about the direction their party has taken in recent years. But if they cross this Rubicon, they will be as culpable as Sen. Cruz or Trump themselves, having resigned any claim to leadership and enlisting as foot soldiers in a radical effort to obstruct and delegitimize the president at all costs.

Republican presidential candidate Ted Cruz says the passing of Supreme Court Justice Antonin Scalia is one reason why GOP voters need to vote him into the White House. (Reuters)

I understand that this is a strategy born of necessity, not strength. My Republican colleagues fear the right wing of their party. But I would ask my colleagues: Are the cheering of Trump’s crowds or the adulation of Sen. Cruz’s acolytes worth sacrificing your basic constitutional duty? Are these the forces you went into public service to serve?

If there were ever a time to take a stand for moderation and common sense, this is it.

[Read more: Justice Scalia’s death and the case for Supreme Court term limits]

I have participated in my fair share of fights over the judiciary. But throughout them all, we always guaranteed Supreme Court nominees a fair hearing and a floor vote. Even nominees such as Robert Bork, whom Democrats vehemently opposed, were given that basic courtesy.

Indeed, in the most recent debates over the judiciary, Democrats’ actions have been aimed at guaranteeing fair votes for as many qualified nominees as possible. In response to unprecedented Republican obstruction, Democrats changed the Senate rules in 2013 to allow qualified nominees to be confirmed by a simple majority vote, instead of 60 votes. This change alleviated judicial emergencies across the country by allowing a flood of qualified nominees to be confirmed. (We stopped short of changing the threshold for Supreme Court nominees — maybe that was a mistake.) If Republicans proceed down this path, one side effect will be settling that debate once and for all and proving that Republican obstruction is so extraordinary — so historically unprecedented — that this “nuclear option” was indeed necessary. That said, I would much rather be vindicated in some other way.

I urge my Republican colleagues, for the good of the country and the sanctity of the American system of government, to recall what Sen. Grassley said only a few short years ago: “A Supreme Court nomination isn’t the forum to fight any election. It is the time to perform one of our most important Constitutional duties and decide whether a nominee is qualified to serve on the nation’s highest court.”

Those words are as true today as when they were first spoken. Pursuing their radical strategy in a quixotic quest to deny the basic fact that the American people elected President Obama — twice — would rank among the most rash and reckless actions in the history of the Senate. And the consequences will reverberate for decades.

The writer, a Democrat from Nevada, is Senate minority leader.