Some have noted language in executive privilege decisions suggesting that protection of presidential communications is greater where the subject is national security or diplomacy. But there is certainly no warrant for the idea that a president’s misconduct is specially immune from scrutiny in the very areas where his corruption may prove most dangerous.
If a president could prevent Congress from hearing the best, and perhaps only, direct testimony about his own misdeeds by the simple expedient of saying the magic words “executive privilege,” the impeachment power would be effectively neutered. The Framers contemplated no such absurdity.
That said, a claim of executive privilege could create procedural havoc, depending on where Trump tried to assert it. If Trump’s counsel raised the issue during the Senate trial, it would be addressed by the chief justice, like any other objection, with a majority of the Senate having the last word. But if Trump went to court to seek to block testimony from his current or former aides, it could at least cause some delays.