There's not really that great of presdence for criminal charges (or civil charges) brought against a sitting president. Normally, criminal charges are processed through Congress.
However, Congress is stacked with the same party as Trump... they're refusing to remove their own man.
Also, the Supreme Court is being stacked. A couple decades ago, I'm pretty sure the SCOTUS would rule that the president of the United States can stand before a trial. If the GOP (and Trump) gets their way, Trump will have nearly unlimited authority.
It doesn't help that Trump's a pathological liar. For example, from one of his speeches recently, they broke out everything he said.
The President can only be impeached. The president is immune from standard criminal prosecution. He could be charged for wrongdoing after leaving office, but he would have to be impeached and removed, or resign. If Trump committed any federal crimes, then only Congress can address that wrongdoing by impeaching him.
It appears from history that only blowjobs and undeniable embarrassing evidence results in modern day impeachment.
Johnson was impeached but acquitted. Nixon was impeached but resigned. Clinton was impeached but acquitted.
The problem with impeachment is that it carries a heavy political repercussion. Even the Democrats (if in majority) will try to avoid it because it is only successful if two thirds of congress vote to impeach. This would require Republicans to vote for impeachment - something unlikely to happen unless there is overwhelming evidence and at least three people recorded it happening. Even then there will be conspiracy theories.
Stacking the Supreme court has been done by both the Republicans and the Democrats. Constitutional interpretation is very important when determining whether laws are valid or not. The Supreme court has extreme powers by declaring something unconstitutional they can effectively nullify a law passed by congress.
Trump has gotten his way all his life using whatever means he could. Teflon Trump - scandals don't stick.