Hearsay would not hold up in a court of law, unless the force of public opinion is so strong against the person so as to overwhelm the need for strong evidence. Even if it were, I don't think it would make for good policy. As you may be familiar with the song by Johnny Horton, "Johnny Reb":
.
When Honest Abe heard the news about your fall
The folks thought he'd call a great victory ball
But he asked the band to play the song "Dixie"
For you Johnny Reb and all that you believed
.
Lincoln did not gloat, and he did what was necessary to prevent the issue from spiraling upward, onward . . . taking Trump out in an underhanded way could prove to be extremely counter-productive, and, in my opinion, we should let the voters decide. Quite frankly, I don't think Trump has a chance in hell of winning, because he has offended far to many people, and they will not forget it. His childish behavior is what un-defines him for the office of president. When he ran for president, few likely noticed, that he used all the trappings of appearing presidential, you did not see him speaking without a flag behind him, and often when he appeared he appeared as if he were already in the White House . . . . something I mentioned to Jill Stein, but evidently she could not understand why it was so important. Now he is in office, but he is destroying the very appearance of being presidential. I say come voting time, he is outta there . . . fired, mostly by his own stupidity.

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I think a whistle blower is not the same as a witness. A whistle blower can report hearsay or even gossip but that doesn't matter because the whistle blower only reports the issue to an investigator who follows up and finds credible independent evidence that substantiates the claim. It is that evidence the perpetrator must answer to (not the whistle blower).

Unfortunately, Congress, the Senate and this POTUS don't have to follow the law.