In Mr. Trump’s case, it refers to the specific allegation that members of his campaign worked with Russia to sway the 2016 election in his favor. But he has adopted it as a shorthand to encompass any allegation against him, making it into the sought-after object in his own kind of morality tale.

In it, there are villains: Mr. Mueller and his “17 angry Democrats,” as Mr. Trump is fond of calling the special counsel’s team, as well as Jeff Sessions, whom he casts as the weak-kneed attorney general who has allowed biased prosecutors to run amok with their “witch hunt.” Michael D. Cohen, his longtime lawyer who pleaded guilty last week to campaign finance crimes and implicated Mr. Trump in the scheme, has also recently joined this team, as the president made clear in several tweets after his plea.

There are heroes, such as himself and the “brave” Paul Manafort, his former campaign chairman, who was convicted of multiple counts of fraud on the same day as Mr. Cohen’s bombshell. Mr. Trump lavishly praised Mr. Manafort for refusing to “break” and cooperate with federal investigators.

And then there’s the Ultimate Prize — the collusion — that nobody seems to be able to lay their hands on, like so many children at a Passover Seder hunting for the afikomen, the hidden piece of matzo at the end of the meal that fetches its finder a reward of a dollar or so. Who can find the collusion, kids?

Nobody yet, even as the buzzer of the midterm congressional elections draws closer.

On Tuesday in West Virginia, collusion hide-and-seek appeared to be little more than a way for the president to shrug off a series of damaging developments; Mr. Trump quickly moved on to other subjects. But his rhetorical questioning also revealed how Mr. Trump, a president facing the most serious of threats, has sought to minimize and trivialize what is happening in and around his White House, and in the process, to desensitize his supporters to grave charges.

“There is an entertainment aspect to this, and this tease of ‘Who’s going to win? Who’s going to be the bad guy?’ and Trump has a demonstrable instinct for this,” said Mary E. Stuckey, a professor of communications at Penn State University who has written extensively on presidential communication. “It keeps people watching, and it puts the attention where he wants it, which is, ‘Where is the shiny object?’”