Robert Mueller is winding down his investigation. The president (liked Nixon) asked to stop being investigated. He is going to be found guilty of more than a handful of crimes.
If he is smart, like Nixon, he will step down in exchange for a blanket pardon at the Federal level.
#1 A presidential pardon is only available for Federal crimes. State convictions, such as some of what the SDNY is going after, cannot be pardoned by any President.
#2 Any federal criminals pardoned by the president lose any immunity granted under the 5th amendment for those crimes (since they can no longer be prosecuted for them). So, once pardoned, they can be subpoenaed by a prosecutor or by Congress, and they have to answer questions, or do time for contempt until they do. Any new acts of perjury committed in new testimony would be new crimes that can then be prosecuted.
Compared to Trump, Nixon was basically just guilty of Federal jaywalking. Trump might well become the first president to trade the Oval Office in for a prison cell; regardless of whether he is impeached (and then convicted by the Senate) or not.
Trump is trapped in a box. I don't think he is going to pardon anyone. And if he doesn't run for -- and WIN -- a second term, the statute of limitations will not yet have expired for whatever he might be guilty of when he leaves (or is ejected from) office. In other words, he can't resign, unless he actually is the innocent lamb he pretends to be. And all indications are that his possible connections to many criminal activities within various jurisdictions cannot all be pardoned by a succeeding president; whomever that might turn out to be.