Trump has committed high crimes and misdemeanors against the United States and must be held accountable.
High Crimes: Collusion
Trump and his campaign have likely committed federal conspiracy by meeting with Russian officials during his campaign. Jared Kushner met with a Kremlin-linked lawyer in Trump Tower with hopes of finding dirt on Hillary Clinton which would have been illegal had the lawyer given them any information. During the transition period before Trump officially took office, Jared Kushner tried to establish a back-channel line of communication with Russian officials to try to avoid federal surveillance.
High Crimes: Obstruction of Justice
Trump also admitted to firing former FBI Director James Comey because the FBI was investigating him which, while it wasn't under oath, it was an admission to Obstruction of Justice. Trump later clarified, saying something completely different by saying that he fired Comey because Deputy Director Rod Rosenstein recommended he do so. Trump has also claimed that he fired Comey because of how he handled the Clinton investigation during the campaign.
Misdemeanors: Violation of campaign finance laws
Trump's former lawyer, Michael Cohen, pled guilty to illegal campaign contributions "in coordination and at the direction of a candidate for federal office." Trump directed Cohen to break federal law to pay Stormy Daniels not to go public with her claim that she slept with him while he was married to Melania. Cohen is now reportedly looking to flip on the President in exchange for a lesser sentence.
Misdemeanors: Violation of the Emoluments Clause
The Emoluments Clause of the Constitution dictates that elected officials can't receive gifts from foreign governments while in office. Trump is currently being sued by 200 Democrats who allege that he is violating the Emoluments Clause by hosting foreign leaders in his hotels. He has attempted to skirt consequences by put his assets into a trust that is managed by his sons but he has also made them his advisers and that obviously violates the spirit of the clause. In fact, Jared Kushner, Trump's son-in-law, had to have his security clearance downgraded because foreign governments were conspiring to blackmail him by using his finances against him. That situation is exactly why the Emoluments Clause is in the Constitution.
He has stoked violent flames
Trump has attacked the media, his political opponents, and minorities with all the grace, tact, and frenzied recklessness of a headless chicken. Since announcing his candidacy, Nazis have murdered in his name and he has refused to condemn them and hate crimes against Muslims have hit a level higher than they did just after 9/11. I, personally, have seen a rise in anti-Semitism as someone spray painted Swastikas on the front of a local school and the Holocaust Museum in Boston was vandalized twice during the summer of 2017. People are dying and unsafe because of him and he refuses to stop his attacks.
We have the ability to remove a President. If we don't use it on such an obviously corrupt one then we'll never use it on anybody and the American people will just end up being taken advantage of again.