Julian Zelizer is a professor of history and public affairs at Princeton University, and author, with Kevin Kruse, of the new book " Fault Lines: A History of the United States Since 1974 ." Follow him on Twitter at @julianzelizer. The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) This week the White House informed Democrats in Congress that they had no constitutional right to investigate whether President Donald Trump obstructed justice. It was the latest of Trump's efforts to ratchet up his claims of presidential power, and it prompted House Judiciary Committee Chairman Jerrold Nadler to declare that the White House was trying to make the President into a king.

Responding to White House counsel Pat Cipollone's letter to Nadler saying that his obstruction investigation was "outside" the constitutional rights of the House, Nadler argued that the White House was taking a stance that is "unprecedented and unsupported by law, history and practice."

When critics of the administration warn of the imperial way in which Trump is attempting to use his power, some defenders point out that other presidents have also flexed their authority extravagantly in recent decades. All presidents have acted this way toward Congress, they say.

The President's supporters have a point. It is true that the presidency has become much more imperial as an institution over the course of the 20th and 21st centuries. Even after post-Watergate reforms in the 1970s attempted to rein in what historian Arthur Schlesinger Jr. in 1973 called the " imperial presidency ," the executive branch has rebounded and continued to expand in strength.

But while the presidency is imperial, we have seen four major precedents that Trump is setting into place that could have enormous long-term consequences on the institution.

Precedent 1: Delegitimating oversight

What has taken shape in recent weeks is an argument suggesting that almost no oversight is legitimate unless the President agrees to a congressional investigation. Even without invoking executive privilege, Trump has been firm he will not cooperate with almost any of the investigations taking place.

Unlike previous presidents who have resisted specific oversight investigations -- and who have tried to hold back specific sets of advisers and documents based on executive privilege -- Trump has argued he has blanket authority to say no to the demands from all congressional oversight operations anytime he wants to do so.

Simply deeming an investigation to be partisan, a claim that most presidents have made when under the spotlight, in his mind appears to be sufficient to undermine the right of Congress to oversee his office.

This claim comes on top of an unprecedented campaign to obstruct a major investigation into Russian efforts to interfere in the 2016 election. If Trump's posture is legitimated by Congress and the courts through their own inaction, this decision would constitute a major step in significantly eroding the ability of the capacity of the legislative branch to hold the president accountable.

Precedent 2: Using the bully pulpit for disinformation

Trump has also gone beyond his predecessors when it comes to using the bully pulpit to propagate disinformation. Of course, it is important to recognize that almost every president lies, as The Nation's Eric Alterman notes in his forthcoming book on the subject, "Lying in State: Why Presidents Lie and Why Trump Is Worse." Some of their lies have been small, and others have been big ones that led us into major wars such as Vietnam and Iraq. But Trump lies in a different, more sweeping and indiscriminate way.

According to The Washington Post, the President has made more than 10,000 lies or misleading statements . He spreads false information without any sense of shame and with a regularity that normalizes this action. His use of what Theodore Roosevelt called the White House's "bully pulpit" in this fashion is part of a political strategy. He spreads false information, conspiracy theories and outrageous accusations to confuse public debate, direct the national media focus and undermine the legitimacy of his opponents.

We saw this use of presidential power early on with Trump's false claims about the size of the crowd at his inauguration, and watched it grow exponentially into the realm of public policy. The reckless abandon with which he uses his presidential platform to pollute the public discourse with falsehoods is a brazen and aggressive use of authority.

Precedent 3: Legitimating conflict of interest

Trump has also used his power to legitimate a massive, unprecedented conflict-of-interest problem at the heart of this administration. One of the biggest dilemmas with the Trump presidency from his earliest days was his refusal to disclose tax information and then his resistance toward creating a serious firewall between his presidency and business. Rather than give up ultimate control of his company, he would only go so far as to put his sons in charge of the business, which meant little in practice.

While other presidents have been accused of conflict of interest (such as Lyndon Johnson and his wife, Lady Bird, with the television stations that they owned in Texas), never has there been a conflict situation of this scale and scope. The President's ownings are directly related to major policy decisions that he makes on a regular basis, including foreign policy.

The use of Trump resorts for presidential weekends and the fact that Trump International Hotel in Washington is a favorite stop for overseas dignitaries from countries such as Saudi Arabia exposes the problematic structure he kept in place. The President's insistence that the business did not have to be broken up or placed far away from his immediate family was a raw assertion of power.

Precedent 4: Using national emergency power to replace legislating

Trump has been imperial with his power in other ways, such as his using executive power to roll back government policies and unilaterally withdrawing from international agreements, such as the Iran nuclear deal. Though this use of executive power is certainly not new among presidents, there have been instances when he has gone well beyond others who came before him. But the President's decision to invoke national emergency power to obtain funding for a border wall that Congress refused to fund several times is the most egregious example of how freely he is willing to flex his authority. If the courts don't strike it down, this will offer a model for future Democratic and Republican presidents to obtain monies that they want without congressional approval.

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Every time that presidents expand the power of the office and Congress fails to respond, the institution of the presidency becomes stronger. Unlike the 1970s, currently strong partisanship has been offering Trump a clear playing field as he moves forward in his imperial presidency. There has been essentially no Republican pushback to this point.

The GOP's blind loyalty to the President has been a big disincentive for House Democrats to pursue impeachment proceedings, as they fear their efforts will be stifled in the Senate. Unless Congress figures out a way to push back, the presidency will be much more imperial when Trump is done with his time in office, leaving future Congresses to confront a White House that will be able to inflict much greater damage on other institutions without any sense of restraint.