What is stopping Donald Trump from being impeached is that majority of the people in the House of Representatives are Republican and they want him there as President.
To impeach means to bring charges in Congress which will form the basis for a trial. The US constitution states a president "shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes or misdemeanours".
The process of impeachment is started by the House of Representatives and only needs a simple majority to pass. The trial will be held in the Senate. Two-thirds vote from the House of Representatives for the process to continue.
The impeachment process is pretty straightforward. The impeachee would first have to commit a high level crime such as treason or bribery. Next the House of Representatives votes on the case of impeachment. Here, majority rules.
Then the case is run by the Senateand resided over by the Chief of Justice.This process is purely political. I believe what is primarily stopping Trump from being impeached is thatthe House of Representatives is majority republican.