There were no contacts between the campaign and foreign governments.
Oh, wait... There were no contacts with Russians.
Oh, wait... There were contacts with Russians but they weren’t improper.
Oh, wait... The Trump Tower meeting was about adoption issues.
Oh, wait... The Trump Tower meeting was about routine “opposition research.”
Oh, wait... The Russians never produced the material they’d promised, so it doesn't matter.
Oh, wait... There’s nothing improper about accepting opposition research from a foreign adversary. Collusion is legal.
Each defense has lasted until facts emerged to render it inoperative.