Julian Zelizer, a history and public affairs professor at Princeton University and a CNN political analyst, is the author of " The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society ." He's co-host of the "Politics & Polls" podcast. The opinions expressed in this commentary are his own.

(CNN) Forty-five years after the June 17, 1972, break-in at the Democratic national headquarters that started the Watergate scandal, the nation finds itself once again in an explosive situation revolving around the potential abuse of power by a commander in chief.

President Trump is creating a dangerous atmosphere in Washington. The underlying scandal in Watergate involved the break-in of the Democratic headquarters. We still don't know if there was collusion between the Russians and the Trump campaign -- though if this did happen, Watergate would feel like small potatoes.

The big similarity, however, is that the effort by the President to stifle the investigation is blowing up into the largest problem of all.

With the President's anguished tweets and the statements of Trump associates like Christopher Ruddy and Roger Stone, the special counsel's investigative task becomes more difficult day by day. This is a dangerous state of affairs, because special counsel Robert Mueller is not fully independent of the administration.

Once Congress allowed the law which provided for creating a special prosecutor to expire in in 1999, the US no longer had an independent, nonpartisan person who could investigate executive branch conduct.

In order to avert another "Saturday Night Massacre," the infamous moment when President Richard Nixon ordered the firing of special prosecutor Archibald Cox, who was looking into the Watergate scandal, we now depend on the expectation that presidents will allow investigations into wrongdoing to take place unimpeded.

While presidents have considerable leeway to attack legislators who are holding hearings, it is vital that the Justice Department, the FBI and appointed special counsel don't feel threatened as they attempt to find out whether something illegal has taken place.

President Trump is not fulfilling this expectation. There is ample evidence, some taking place right before our eyes, that he is pressuring and intimidating government officials whose jobs still depend on his good graces.

The intimidation began with former FBI Director James Comey. While President Trump and his supporters have gone to great lengths to downplay Comey's claims that he felt the President was placing improper pressure on him to stop looking into all things Russia, for many observers the defense doesn't really pass the smell test.

JUST WATCHED Russia investigation takes new twists Replay More Videos ... MUST WATCH Russia investigation takes new twists 05:54

After all, the fact that Comey felt so uncomfortable being alone with President Trump is already evidence that something was wrong. Though the President's defenders say that the word Comey said Trump used -- "hope" -- in expressing a desire for the Michael Flynn investigation to end doesn't really mean much, in this context, and said to someone who served at the wishes of the President, the signal seems pretty clear.

This is particularly true since the story culminated with the President actually firing Comey. After the initial excuse that the decision came because of how he handled the Hillary Clinton email investigation, the President then admitted on television that he did this to stop the "Russia thing" and then told the Russians behind closed doors he was relieved to have the pressure of the investigation off his back.

Trump's next target has been Mueller, the former FBI director and special counsel who has been expanding his investigation into the 2016 campaign and into obstruction of justice.

Mueller, who is not totally independent of the President, either, has been the subject of attack. President Trump's close friend, Christopher Ruddy, sent out an ominous message when he suggested the President was considering firing him.

The White House distanced itself from the notion in the face of a backlash, but many observers suspect Ruddy was delivering a message straight from the Oval Office.

And one day after the horrendous shooting directed at Republican congressmen playing baseball, the President could not contain himself and blasted out a tweet about the "single greatest WITCH HUNT in American political history --led by some very bad and conflicted people."

Friday, the next Trump victim was yet another appointee, Deputy Attorney General Rod Rosenstein. "I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt." Now admitting that he was the subject of an investigation, Trump's tweet will send a strong message to Rosenstein, who has to balance overseeing the investigation with his boss lashing out about what he is doing.

President Trump shouldn't be wondering why there is an investigation into the obstruction of justice. Some might say he is obstructing justice right in front of our eyes.

The comparisons to President Clinton's attacks on Kenneth Starr and to Reagan administration officials who criticized Lawrence Walsh miss the fact that both of those prosecutors were independent under the 1978 Ethics Law, which no longer exists.

Now we are back to where we were in the dark days of 1973, and President Trump is flexing his muscle in way that even President Richard Nixon would have been hesitant to do.

The officials responsible for determining if the President and his advisers abided by the law must work every day knowing that their future might be on the chopping block if they carry out their responsibilities.

Follow CNN Opinion Join us on Twitter and Facebook

All of this goes on because the Republicans in Congress remain quiet. The press and congressional Democrats have been pretty forceful in saying that something is going very wrong. Republicans in Congress, however, have generally focused on leaks from the investigation and justification for why Trump might have just been careless or naive rather than what is right before their eyes.

It's time for some profiles in courage on Capitol Hill. Regardless of whether Republicans believe that the President or his associates are guilty of anything, there must be some who understand why a legitimate investigation is vital.

Without such an investigation, the President, ironically, will never be able to clear his name. We have reached the point where our democratic institutions are now in dire need of bipartisan demands for accountability, with members focusing on the national interest above anything else.

When prosecutors and Congress looked into what happened in the Watergate break-in, President Nixon's response was ultimately what brought him down. With each tweet and tirade, President Trump might very well be following in his footsteps.