Here are some reactions to the decision he announced on Wednesday, ranging from praise for the role of his long conservative track record in shaping the judiciary to criticism over what some saw as his inability to push back against former President Donald Trump:

DEMOCRATIC US SENATE MAJORITY LEADER CHUCK SCHUMER

"During my years in the Senate, Mitch McConnell and I rarely saw eye to eye when it came to our politics or our policy preferences. But I am very proud that we both came together in the last few years to lead the Senate forward at critical moments when our country needed us."

REPUBLICAN US SENATOR THOM TILLIS

"Under his historic leadership, the Senate secured a conservative majority on the Supreme Court, passed historic tax reform, and enacted bipartisan legislation to save our economy from the brink at the start of the pandemic. He has stayed true to President Reagan's principle of peace through strength."

REPUBLICAN US HOUSE SPEAKER MIKE JOHNSON

"No member of Congress has played a greater role in reshaping the federal judiciary than Mitch. I join my colleagues in saluting his historic contributions to the Republican Party and to the Congress. His legacy will endure for generations."

REPUBLICAN US SENATOR JOHN THUNE

"He leaves really big shoes to fill. ... I kind of just want today to honor him."

REPUBLICAN US SENATOR MITT ROMNEY

"No senator in memory has demonstrated more respect for the institution of the Senate than @LeaderMcConnell. ... Leader McConnell has been steadfast in his defense of conservative values, promoting a conservative judiciary, invigorating economic growth, insisting on America's defense of freedom, and the protecting the rights of all Americans."

REPUBLICAN US SENATOR LINDSEY GRAHAM

"Senator McConnell will be remembered as one of the most effective leaders in the history of the U.S. Senate. Through sheer force of will, he has shaped the federal judiciary in a conservative fashion."

REPUBLICAN PRESIDENTIAL CANDIDATE NIKKI HALEY

"I respect Sen. McConnell's decision. Serving at that level for that long is not easy. He did many good things, but he is right that we do need a new generation, not just in Congress but also in the White House."

SHANNON WATTS, FOUNDER OF ACTIVIST GROUP MOMS DEMAND ACTION

"Sen. Mitch McConnell's legacy will be that he purposefully undermined America's first Black president, he broke the Supreme Court, he helped elect a fascist President, and he abetted up an insurrection on American soil."

ANTI-TRUMP GROUP THE LINCOLN PROJECT

"Mitch McConnell will go down in history as a spineless follower who cowered to a wannabe dictator clown. He chose the power of a tyrant over protecting democracy. When you remember him, remember this."

DEMOCRATIC US REPRESENTATIVE ADAM SCHIFF

"Mitch McConnell stacked the Court, undermined our democracy, and enabled Donald Trump. And yet - in his absence - the @SenateGOP will invariably select someone more extreme."

(Reporting by Kanishka Singh, Susan Heavey and Katharine Jackson in Washington; Editing by Lisa Shumaker)

By Kanishka Singh