That nothing has been proven against Trump during his time in office is, more or less, the point we're debating here: while President, the very office shields him from legal scrutiny. He has been able to drag through the courts, as least twice, even the attempt to look at his tax returns, which may (or may not) demonstrate certain financial irregularities -- although his choice to hide behind the legal power of the Federal Government, and the phony excuse of being "under audit" are, at least, suggestive. Ditto several claims of rape or sexual assault: Trump has attempted to block DNA evidence being used against him, which is also odd considering that this would quickly exonerate him if no match were found.
I could also point to the Impeachment. No doubt it was politically motivated to start proceedings, but it was also politically motivated to stop them, and the whole process was a waste of time and effort in terms of uncovering the truth.
I could also point to the Mueller report, whose language was careful in not exonerating Trump, instead making it clear that there was a case to answer for obstruction of justice, assuming Congress were to bring it.
I could, perhaps, also point to the many out-of-court settlements that Trump has used over the years to avoid further scrutiny, including, but not limited to, the Trump University scandal (fraud claims settled for $25 million); The Donald J Trump Foundation (fraud claims settled for $2 million, with the foundation also forced to close); and several dozen others over the decades, all of which are too complicated for me to properly understand but most of which seem to involve fraud and general dodginess. Trump has a long and colourful history, in short, and has been lucky that he's had the money to throw at it to stop all the fraud allegations going any further than settlements.