If Mueller gets trump on collusion or any charge, will the senate, house, congress, b COMPELLED to impeach? So far they have resisted and im wondering if they can refuse to impeach.

No.

Procedurally, an impeachment can be brought by a majority vote of the House of Representatives against any civil officer of the federal government.

In practice, the House investigates whether impeachment charges would be warranted. If it determines that charges are warranted, articles of impeachment are drafted that specify the various charges against the officer in question and those are voted on by the whole House.

Once the Senate receives articles of impeachment from the House, it organizes itself into a court. Senators take an oath to do “impartial justice according to the Constitution and the laws” when sitting as judges in that court, and the chief justice of the United States presides over the court in the case of an impeachment of the president. The House appoints managers to prosecute the case before the Senate, and the impeached officer is entitled to present a defense. At the conclusion of the trial, the members of the Senate must vote on each individual article of impeachment. Conviction requires a guilty verdict from two-thirds of the participating senators.

Upon conviction, the Senate may impose a punishment of removal from office or disqualification from any future federal office.

www.theatlantic.com/politics/archive/2017/05/a-primer-on-the

Another good site:

http://www.abc.net.au/news/2017-12-05/how-does-impeachment-work/8615086