CONCORD, N.H. — There is a phony political contest going on here, just below the radar, that Joe Biden can only lose.

He almost certainly won’t; but there’s danger anyhow in the companion to the bruising New Hampshire primary, where four Republicans are desperately trying to defeat a former president, Donald Trump, but probably won’t.

Biden’s allies — mostly establishment Democratic figures, some of whom might welcome his withdrawal — are ramping up a write-in campaign in New Hampshire to permit him to prevail in a contest that he says shouldn’t matter and that he took steps to ensure wouldn’t matter — unless of course he loses.

Months ago, the president, who finished fifth here in 2000, ordered Democrats to begin their primary contests in South Carolina rather than New Hampshire, which has held the first primary for more than a century. Thus the results of this month’s contest won’t count in the struggle for delegates at the Democratic convention.

But he, or rather his surrogates, are competing anyway. Just the other day, Gov. J.B. Pritzker of Illinois — ssshhhh! He might run for president if Biden demurs — sent out an appeal to Democrats arguing this write-in campaign was “truly, vitally important.”

This is a big risk, even if Biden’s opponents are the self-help author Marianne Williamson and little-known Rep. Dean Phillips of Minnesota. New Hampshire will allow pretty much anyone to vote in the GOP primary, and Trump opponents might be happier casting a ballot for former Gov. Nikki Haley than a meaningless write-in for Biden.

And then there is the 1968 flashing caution light.

President Lyndon Johnson didn’t compete in New Hampshire then, but a similar write-in campaign was underway anyway. Johnson’s team was worried enough to conduct private polls that suggested his lone opponent, Sen. Eugene McCarthy of Minnesota, might manage 18%. “I never allowed my name to go on the ticket in New Hampshire,” the president said later in an oral history for his presidential library. “If I had, I have no doubt that I would have won New Hampshire 2-to-1.”

But he didn’t, and he didn’t.

McCarthy came within 230 votes of defeating Johnson.

There was trouble for LBJ from the start. “He had never spent a winter’s morning standing outside the Brown Paper Co. in Berlin greeting workers arriving for their shift,” Charles Brereton wrote in his 1987 “First in the Nation.” “Nor had he ever strolled up and down a Main Street greeting shoppers or merchants.”

Two days before the primary, Johnson bid Lady Bird to their bedroom. He had gone for a nap but couldn’t sleep. Maybe it was because of the conversation the couple had had earlier in the day. She asked him, not in a querulous way but in a curious way, “Suppose someone else were elected president, what could ‘X’ do that you could not do?”

Johnson’s answer: “He could unite the country and start getting some things done. That would last about a year, maybe two years.”

In her diary, Mrs. Johnson engaged in deep reflection. “I think that is what weighs heaviest on Lyndon’s mind. Can he unite the country, or is there simply too much built-up antagonism, division, a general malaise, which may have the Presidency — or this President — irrevocably as its focal point?”

A month earlier, U.S. News and World Report had said, “At this point, there is just one near certainty about the ‘68 elections ... Lyndon Johnson, health permitting, will be the Democratic nominee.” Chicago Daily News columnist Carl Rowan wrote at about the same time that the chances that the president wouldn’t run “can’t be better than a million to one.”

The Johnsons — husband and wife, daughters Lynda and Luci — had discussed the trajectory of the presidency frequently, repeatedly vetting the question of whether they might leave the White House at the end of Johnson’s first term, in January 1969. Mrs. Johnson was clear-eyed about it; one full term was enough. Luci worried about her father’s health. Lynda preferred that he demur. As early as September 1967, 14 months before the election, press secretary George Christian was noodling around with a withdrawal statement. Gov. John Connolly was recruited to help.

Johnson shared his doubts about another term with, among others, Secretary of State Dean Rusk and Secretary of Defense Robert McNamara. The president was preoccupied with the question of whether the American combatants in Vietnam would feel let down. Gen. William Westmoreland assured him they wouldn’t.

Meanwhile, Horace Busby was working on the language the president might use to announce such a decision, perhaps during his State of the Union Address. Many years ago, Busby, who had become a very good source of mine, told me that he wasn’t sure whether Johnson would use that occasion. In the event, the president forgot to bring the statement with him to the Capitol.

On March 31, in a nationally televised address on Vietnam, he said: “With America’s sons in the fields far away, with America’s future under challenge right here at home, with our hopes and the world’s hopes for peace in the balance every day, I do not believe that I should devote an hour or a day of my time to any personal partisan causes or to any duties other than the awesome duties of this office.”

He said in his memoir: “I had used the power of the Presidency proudly, and I used every ounce of it I had. I used it to establish programs that gave thousands of youngsters a head start in school, that enabled thousands of old folks to live in clean nursing homes, that brought justice to the Negro and hope to the poor, that forced the nation to face the growing problems of pollution.”

He continued, in language that might give Biden jitters, or courage:

“In this exercise of power, I knew a satisfaction that only a limited number of men have ever known, and that I could have had in no other way. Men, myself included, do not lightly give up the opportunity to achieve so much lasting good, but a man who uses power effectively must also be a realist. He must understand that by spending power, he dissipates it.”

A botched write-in campaign helped nudge Johnson out of a reelection campaign.

It could happen again. It probably won’t, but it could.