The check and balance is that he has to get all those people to agree with him. Certainly on major issues where he aligns with Republican philosophy that might happen. But he's not a dictator that can do as he will tomorrow. If he decided he wants to transfer the entire U.S. treasury into his personal bank account he wouldn't be able to.

Certainly I doubt our founders thought an entire political party would control every single branch of government. But even if it does the only things that can be accomplished need to be agreed upon by that large group of people. If the will of the people is to elect a group of people into those positions that all hold the same philosophy and values, then that's just democracy. It's what we voted for. I don't know if any party has controlled all three branches of government at once, but it's not like that negates the principle of checks and balances