President Trump is the head of the Executive Department of the government. The Justice Department and its subsidiary organization the FBI are headed by Trump appointees. You would think if the FBI was to descend on Trump's personal attorney in order to find evidence of election tampering or any other crime tied to Trump that his appointees would certainly have notified him unless, they were just as interested in getting rid of him as the Democrats. The answer to that might also be the answer they are not interested in going after Clinton.
The real problem is they have yet to find an impeachable offense and philandering has already been taken off the table in debacle of Clinton's impeachment.