The writers of our constitution tried to establish a form of government that would make it difficult for a tyrant to take control of our country. They divided the power centers of government into three, executive, legislative, and judicial, each with a check on the other. Madison knew there was a way to undermine their checks and balances. What was not yet on the horizon when he wrote this were political parties, but he described them above as “accumulation of all powers in ...the same hands”, " of many or a few." The "few" today is one party in control of all three branches of government with members unwilling to exercise their Constitutional power to check actions of one another.
Respect of the rule of law is jeopardized. GOP House members believe that law enforcement, the FBI, Justice or the Mueller special counsel, should be staffed by only those loyal to the president to be credible, and that party affiliation of FBI or the Department of Justice leaders and key staff (all Republicans) is not enough. They demand the Department of Justice investigate investigators investigating Trump. Recently they forced the Department of Justice to turn over fired FBI Director James Comey's notes of his meeting with Donald Trump, key to an obstruction of justice case. That is an unprecedented interference by Congress to out evidence of an on-going criminal investigation.
The Senate is a profile in cowardice, like House members afraid of being primaried for being disloyal to the President. With few exceptions, voices raised against Trump by GOP Senators are those who are not standing for election soon or ever. The Senate is currently engaged in fast track approving appointments to the federal judiciary loyal to the president. The suspicion is they are so far refusing to pass legislation to protect Special Counsel Mueller from the president firing him because they do not want their names to go on record. Their rationale, Trump would veto their bills anyway and they could not imagine Trump would fire Mueller or his boss Rod Rosenstein. Oh really?
The other check is a free press with a wide varieties of opinions and presenting facts as they discover and present evidence of them. Trump's bias in favor of Fox News, Breitbart, and Sinclair Media , who often convey his message and support him, is hardly a secret. Trump calls reports that paint him in a bad light as "fake news" from "failing" media. Mueller’s investigation will be issuing a report on the Trump campaign’s coordination with the Russians in the 2016 race, followed by reports on financial crimes. Trump is acting like he fears the report will hurt him and has been vigorously attacking the credibility of the Russian connection DOJ investigators and threatening he will fire them. It appears Trump is taking preemptive measures to destroy the credibility of the FBI as a "deep state" full of partisans against him so that supporters do not take Mueller’s findings as fact. Recently, he tried to punish the owner of the “opposition press”, the Washington Post, by attacking the other business the paper owner has, Amazon , using easily disproved lies.