What a difference an election makes. In February, when Representative Joe Sestak was the insurgent underdog challenging a President Obama-anointed incumbent, he told a Philadelphia-based cable host that the previous summer the White House had offered him a high-ranking federal job if he would drop out of the race. Now that he is the Democratic nominee to replace Senator Arlen Specter, he’d rather talk about anything else.

On NBC’s “Meet the Press” Sunday, David Gregory had to put the question to Mr. Sestak four times before he would even repeat his February assertion. The candidate still refuses to say who allegedly made the offer or what the job in question was. That, he told Mr. Gregory, “is for others to talk about.”

Those others are even more evasive. White House Press Secretary Robert Gibbs said the same day that “lawyers in the White House and others have looked into conversations that were had with Congressman Sestak, and nothing inappropriate happened.” Senior adviser David Axelrod added on Monday that “when the allegations were made, they were looked into, and there was no evidence of such a thing.”

Mr. Axelrod said that offering a job in exchange for Mr. Sestak’s withdrawal would “constitute a serious breach of the law.” But he and Mr. Gibbs, speaking in the passive voice about unidentified people, have not disclosed who held the purportedly innocent conversations with Mr. Sestak, what was said during those talks, or who made the determination that it was not untoward. Imagine if Karl Rove or Alberto Gonzales tried that one.

Mr. Sestak has come under pressure to reveal what he knows, and not only from Republicans like Darrell Issa, ranking member of the House Oversight and Government Reform Committee. Yesterday Senate Majority Whip Dick Durbin told reporters: “At some point, I think Congressman Sestak needs to make clear what happened.”

The White House should come clean too. An effort to clear a primary field would be far from unprecedented, but as Mr. Axelrod acknowledged, it could be a felony if the interference in an election was direct enough. President Obama’s supporters on the left have argued that he needs to be more like Lyndon B. Johnson. “LBJ’s brawling, southern style of trench politics is the one best suited for the current challenge,” wrote one such ally last September. The President’s stonewall suggests he is following such advice.