Mitch McConnell’s announcement that he will not seek reelection next year brings to a close the political career of the longest-serving Senate leader history. He is also the longest-serving senator from Kentucky.

But to what end?

I’ve long viewed McConnell as something of an enigma, regarding him with a mixture of sympathy and disdain. Afflicted with polio as a child, he received treatment at the Roosevelt Warm Springs Institute for Rehabilitation in Georgia, treatment that likely saved him from being disabled for the remainder of his life.

It’s difficult not to have sympathy for a polio survivor. His family “almost went broke” because of the medical costs, he said, yet as senator he led the opposition to Barack Obama’s Affordable Care Act and to the expansion of Medicaid.

During his senior year at the University of Louisville, McConnell attended the March on Washington for Jobs and Freedom on August 28, 1963. He’s been more sympathetic to civil rights than some of his Republican colleagues, yet he also said “there were actually good people on both sides” of the Civil War.

McConnell served as an assistant attorney general during the Ford administration, then returned to Kentucky and began his political ascent. He was elected executive of Jefferson County and won election to the U.S. Senate in 1984.

McConnell arrived in Washington as the least senior member of the Senate. “I was just happy if anybody remembered my name,” he recalled. But he began his ascent into leadership positions, culminating with his election as party leader in 2006.

McConnell was considered a moderate Republican early in his political career, a species now virtually extinct. According to a biographer, Alec MacGillis, McConnell changed “from a moderate Republican who supported abortion rights and public employee unions to the embodiment of partisan obstructionism and conservative orthodoxy on Capitol Hill.”

He adopted the sophomoric trope of referring to the Democratic Party as the “Democrat Party,” and in October 2010, he memorably announced that “the single most important thing we want to achieve is for President Obama to be a one-term president.”

To thwart Obama’s initiatives, McConnell deployed the filibuster to block legislation in the Senate, including health care, campaign finance and banking reform. But his most successful — and deplorable — maneuvering centered on judicial appointments, especially to the Supreme Court.

When Antonin Scalia died in February 2016, nine months before the general election, McConnell declared that, as majority leader, he would not consider Obama’s nominee to replace Scalia. “The American people should have a voice in the selection of their next Supreme Court justice,” McConnell said. “Therefore, this vacancy should not be filled until we have a new president.”

Instead, Donald Trump nominated, and the Republican Senate confirmed, Neil Gorsuch.

But when Ruth Bader Ginsburg died in September 2020, two months before the next election, McConnell hurried Trump’s nominee, Amy Coney Barrett, to confirmation just days before Trump was defeated by Joseph Biden in the 2020 election.

In August 2016, McConnell told an audience in Kentucky, “one of my proudest moments was when I looked Barack Obama in the eye and I said, ‘Mr. President, you will not fill the Supreme Court vacancy.’ ”

McConnell voted against convicting Trump in his first impeachment, but he began finally to sour on Trump following the attack on the Capitol by domestic terrorists on Jan. 6, 2021. After the House of Representatives again passed articles of impeachment, however, McConnell successfully maneuvered to delay a trial in the Senate before the end of Trump’s term.

When the second impeachment trial concluded on Feb. 13, 2021, McConnell once again voted to acquit, arguing that impeachment wasn’t appropriate because Trump was no longer president. “There is no question that President Trump is practically and morally responsible for provoking the events of that day,” he said later. “If President Trump were still in office, I would have carefully considered whether the House managers proved their specific charge.”

Hardly a profile in courage.

Yes, McConnell successfully acquired and exercised power, but to what end? Did his judicial machinations or his toadying to Trump make the nation a better place? I happen to believe that when the history of this political era is written, McConnell will emerge as a villain. If our democratic institutions survive the next four years, which is by no means assured, it will be no thanks to McConnell.

“Mitch McConnell thinks Trump will be remembered as his fool,” Stuart Stevens, a Republican operative and author of “It Was All a Lie,” told Politico, “and I think the odds are pretty good it’s going to be the other way around.”

Randall Balmer teaches at Dartmouth College.