The Justice Department quietly approached Harvard University last month with startling claims, even by the extraordinary standards of the Trump administration’s monthslong assault on the elite college.

The department signaled that it was reviewing claims of discrimination against white men at The Harvard Law Review, and accused the renowned publication of destroying evidence in an open investigation. The administration demanded that Harvard “cease and desist” from interfering.

In a series of letters that have not been previously reported, the government also disclosed that it had a “cooperating witness” inside the student-run journal. That witness now works in the White House under Stephen Miller, the architect of the administration’s domestic policy agenda, Trump officials confirmed.

The Law Review is independent of Harvard University. The allegations nonetheless deepened fears among Harvard officials that the administration appeared eager to escalate one of its civil investigations into a criminal inquiry, underscoring how the university’s problems with President Trump extend far beyond the loss of billions in federal funding.

But the aggressive language in the letters from the Justice Department’s two top civil rights lawyers appeared to have overstated the allegations in pursuit of an additional way to punish Harvard. In that way, the episode fits a broader trend in how the administration is wielding federal investigatory powers to impose its political agenda.

From reshaping the economy to ramping up deportations to punishing the nation’s elite law firms and universities, Mr. Trump’s government has repeatedly prized speed and shock value over the kind of methodical steps typically taken to build a legal case.