Julian Zelizer is a history and public affairs professor at Princeton University, editor of " The Presidency of Barack Obama: A First Historical Assessment " and co-host of the "Politics & Polls" podcast. Follow him on Twitter: @julianzelizer. The opinions expressed in this commentary are those of the author. View more opinion articles on CNN.

(CNN) In The Boston Globe last week, distinguished scholar Andrew Bacevich put forth some strong criticism of President Donald Trump's opponents. He said he increasingly has come to believe that "Trump's election has induced a paranoid response, one that, unless curbed, may well pose a greater danger to the country than Trump himself. This paranoid response finds expression in obsessive attention given to just about anything Trump says, along with equally obsessive speculation about what he might do next."

As opposed to a danger to democracy or a threat to constitutional rights, Trump, in Bacevich's view, is just a "clownishly incompetent and willfully ignorant buffoon."

Bacevich's main point is that despite the fact that many of Trump's statements are "nonsense" and that much of what he does has not produced long-term impact beyond a "single news cycle," his opponents act like the sky is falling with every piece of breaking news. He offers a variation of what the President and others have called "Trump Derangement Syndrome."

International alliances are still in place, Bacevich reminds us, and there are real sanctions on Russia. "America First" has not resulted in US troops leaving hot areas such as Syria or Iraq.

Too many people, he concludes, are consumed with "sensationalistic ephemera" from the White House and are losing sight of key issues such as economic inequality or endless wars abroad.

Bacevich offers a useful warning. Namely, Trump's opponents should not fall into the trap of allowing his frenzied, scatter-shot approach to leadership to cause them to lose focus on what's really going on or to overstate the threats he poses.

Yet as the nation lives through its second summer with a Trump presidency, it would be even more risky to understate the kind of impact that he is having and to write off the genuine sense of alarm as mere paranoia.

Historian Richard Hofstadter was correct to say in his classic 1964 Harper's article that the paranoid style always had a strong hold on certain American political movements, including right-wing, anti-communist conservatism in the early 1950s. "I call it the paranoid style," he wrote, "because no other word adequately evokes the sense of heated exaggeration, suspiciousness, and conspiratorial fantasy that I have in mind." But this is not the psychology that is the driving force behind much of the political mobilization against the Trump administration.

How Trump's tweets change things

Trump's rhetoric should not be quickly dismissed. Presidential rhetoric is extraordinarily consequential. More than almost any other figure in public life, the president has the ability to inject ideas into the body politic and to shape the topics of debate in national life -- and that was true even before a Twitter blast could rivet the nation's attention.

There are many ways in which the President's rhetoric has an impact. While the media is still fully intact and doing its work, Trump has successfully sown doubt and distrust about major news organizations with his talk about "fake news." Ninety-two percent of Republicans, according to an Axios poll in June, believe that the media intentionally produce misleading stories.

While Robert Mueller's investigation continues and the intelligence community still works to stop a future intervention in our election, Trump's ongoing attacks against the legitimacy of these efforts have become a subject of perpetual conversation as well as of very real congressional investigations.

The President's verbal assaults on immigrants, undocumented and legal, matter very much in helping to give legitimation to hard-line rhetoric that many Republicans -- such as George W. Bush -- hoped would remain on the fringes of political life.

Even as he does not literally dismantle NATO, Trump's words do immense damage, raising questions about how the United States would react in a crisis with a president who blasts key allies such as Germany while praising Vladimir Putin for his leadership.

If NATO and the G-7 survive, it is not because Trump's attacks are insignificant, but because leaders in the alliances might work around him.

Real policy changes

The President's rhetoric is not the only real impact that infuriates his opponents. Policy change has mattered very much. When the public saw children being separated from their parents at the border and put into fenced in detention centers, those images should have instantly ended any conversation about his agenda not having huge consequences on the lives of people in the United States and abroad. This is just one example of the many major changes Trump has made.

It is true that the Trans-Pacific Partnership, the Iran nuclear deal and the Paris climate accord are still standing -- but Trump has decided the United States won't be a part of them.

The President has used executive power to roll back important regulations on carbon emissions and on Wall Street while dismantling key parts of the Affordable Care Act in ways that threaten the long-term viability of the program.

The imposition of tariffs on China as well as the European Union has triggered a very real response that can have significant effects on large sectors of the economy -- just ask soybean farmers.

The massive corporate tax cut passed in 2017 will take a huge bite out of the fiscal strength of the government, leaving less money to deal with key national issues such as infrastructure and adding to the debt burden facing younger generations.

The Muslim ban as revised is now in effect. With his second Supreme Court nomination underway, Trump will most likely shift the court sharply to the right.

Presidential inaction also matters. Numerous members of Trump's own administration agree that the United States has not devoted enough resources to protecting our election system. His refusal to push for stronger national gun laws in the aftermath of the Parkland, Florida, school massacre has stifled legislative momentum for regulations to prevent future tragedies.

All of these policy choices and more are very real. One can be concerned, angry or frightened about them without being paranoid.

Trump is also having an important effect within the GOP. He is clearly solidifying and accelerating the sharp rightward drift in the party since Barack Obama took office.

During Republican primaries, we have seen more candidates embrace the President's policies and even style, if not the commander in chief himself. There are fewer voices of dissent.

While the President is not the cause of the party's rightward drift or toward a take-no-prisoners approach to governance, his total embrace of the Fox News-era style of Republican politics is wiping out other kinds of voices in the party. This is highly significant since it has the potential to define one of the two major political parties in such a way that it will continue to espouse his views and style long after he is gone. Trump entrenches Trumpism within the GOP.

Making his opponents look paranoid has in fact been a conscious strategy of the President. This is why he warns that critical news is not real and how a "deep state" is driving the investigation against him.

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Paranoia is certainly a relevant problem in US political history. But Hofstadter's theory doesn't capture most of what is going on with Trump's opponents. Nor does the President when he sweeps aside the critics of his jaw-dropping press conference in Helsinki, Finland, as " haters ."

Brushing aside a majority of the President's critics as showing signs of paranoia misses the new political reality of the Trump administration.