The John F. Kennedy Library Foundation is accepting nominations for its annual “Profile in Courage” award. The award recognizes “a public official . . . at the federal, state or local level whose actions demonstrate the qualities of politically courageous leadership in the spirit” of President Kennedy’s 1956 book by the same name. It tells the stories of eight U.S. senators who risked their careers by taking unpopular stands for the good of the country.

As the U.S. Senate takes up a purely partisan impeachment, and the mainstream media focuses on what Republican senators may do, it may be timely to consult Kennedy’s definition of political courage and why he considered one statesman in particular worthy of admiration.

The sixth chapter of JFK’s Pulitzer Prize-winning book tells the story of Sen. Edmund G. Ross of Kansas, who, in the view of one historian Kennedy cites, performed “the most heroic act in American history.” That deed holds important lessons for our own time. Ross won Kennedy’s esteem by defying his own party’s effort to oust a sitting president.

Andrew Johnson had been elected as Abraham Lincoln’s vice president in 1864 and served alongside him until the Great Emancipator was struck down by an assassin’s bullet in April 1865. Although he ran on the same ticket as the first Republican president, Johnson was a longtime Democrat who refused to abandon the Union when his home state of Tennessee seceded in 1861. It was no surprise, then, that after a bloody Civil War, he shared Lincoln’s desire to bring the Southern states back into the fold as soon as possible. Early in his presidency, Johnson made clear that he would continue Lincoln’s policies.

The new president quickly ran afoul of the Republicans in Congress, who wished to impose a far harsher penalty on the former Confederacy. They grew increasingly impatient with Johnson after he vetoed several pieces of Reconstruction legislation, and they hatched a plot, in Kennedy’s words, to “accomplish their major ambition, now an ill-kept secret, conviction of the president under an impeachment and his dismissal from office!”

They found their grounds in a rather pedestrian law, the Tenure of Office Act, which asserted, on dubious constitutional grounds, that the president could not remove an appointed executive-branch officer without Congress’s authorization. In August 1867, President Johnson fired War Secretary Edwin Stanton, whom he’d inherited from Lincoln, and replaced him with Gen. Ulysses S. Grant.

With public opinion running against Johnson, the Republicans pounced. In February 1868, the House quickly approved articles of impeachment, voting 126-47 along party lines.

Attention soon turned to the Senate. Republicans also held a majority, but not the two-thirds required to convict. None of the 12 Democrats would vote in the affirmative, and of the 36 votes necessary to convict, Republicans were certain of only 35. Six Republicans had already declared their opposition. Ross was the lone holdout.

He had supported emancipation from the beginning. In 1854, when he was 28, he helped a mob rescue a fugitive slave in Milwaukee. Two years later he joined the rush of antislavery settlers to “bleeding Kansas.” In 1862 he enlisted in the Union Army, where he rose to the rank of major. And in 1866, he introduced resolutions at a mass meeting in Lawrence, Kan., that condemned then- Sen. Jim Lane for supporting Johnson on several key votes.

But once Johnson was impeached, Ross was determined to render a fair judgment, resisting his own party’s stampede. After he told a colleague he wouldn’t let his political leanings affect his decision, word spread throughout the caucus that Ross was “shaky.”

The Republicans came down on him hard. “Ross and his fellow doubtful Republicans were daily pestered, spied upon and subjected to every form of pressure,” Kennedy wrote almost a century later. “They were warned in the party press, harangued by their constituents, and sent dire warnings threatening political ostracism and even assassination.” One Republican opponent of the partisan impeachment called these actions of the House Republicans “madness.”

The pressure was almost unbearable. As Ross later described it, “I almost literally looked down into my open grave. Friendships, position, fortune, everything that makes life desirable to an ambitious man were about to be swept away by the breath of my mouth, perhaps forever.”

But at the close of the trial on May 16, 1868, he stayed true to his convictions, opposed the passions of his own party, and voted to acquit Johnson. He faced social ostracism and physical assault. Still, he knew he was right. To give Congress such power over presidential appointments, he later wrote, would have “revolutionized our political fabric into a partisan Congressional autocracy.” He was vindicated in 1887, when Congress repealed the Tenure of Office Act, which the Supreme Court later declared unconstitutional.

By the time he died in 1907, the public view of his role in Johnson’s impeachment had changed. As Kennedy wrote, “those Kansas newspapers and political leaders who had bitterly denounced him in earlier years praised Ross for his stand against legislative mob rule.”

In his book, Kennedy borrows his definition of courage from Ernest Hemingway : “grace under pressure.” Edmund Ross showed such grace on that fateful day in 1868. Will we see it again?

Now, as all eyes turn to the U.S. Senate and another partisan impeachment, and the parallels between Ross’s time and our own are striking.

Then as now, a political faction has forced a partisan impeachment through the House in the heat of an argument over a difference in policy. Then as now, this faction has cheapened the impeachment process, which the Founders believed should be reserved for only the most grave abuses of the public trust.

But despite the focus on what a handful of Republican senators may do, the true profile in courage, as Kennedy understood it, would be a Senate Democrat willing to stand up and reject a partisan impeachment passed by the Democrat-controlled House.

The question naturally arises: Who, among the Senate Democrats, will stand up to the passions of their party this time? Who will stand up against “legislative mob rule” and for the rule of law? Who will be the 2020 Profile in Courage?

Mr. Pence is vice president of the United States.

This op-ed appeared in The Wall Street Journal on January 16, 2020