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) Standing in Warsaw Square, the site of the famous Polish rebellion against the Nazis during World War II, President Trump delivered one of his most effective speeches .

Following a chaotic press conference, which devolved into more discussions about "fake news" and President Obama's failures, President Trump called on the West to "defend our civilization."

During the speech, he offered more coherence than usual with a road map for US policy. He said he would defend Western values against the threat that they faced from terrorism, that the US would adhere to Article 5, which commits members of NATO to defend each other from attack, and he condemned Russian efforts to destabilize other countries.

"We urge Russia to cease its destabilizing activities in Ukraine and elsewhere...." The Polish government also made certain that the optics worked in his favor, with supportive crowds having been brought in who chanted "Donald Trump!" and "USA!" throughout.

There will be many critics of key components of the substance of the speech. His belief that this is a battle of civilizations, between the West and "radical Islamic terrorism," is sure to draw fire from those experts who don't believe it is correct or useful to frame the threat in this particular fashion. There will also be observers who wonder why the President would elevate the conservative critique on bureaucracy into his doctrinal speech about the fate of Western civilization.

Regardless of the policy disagreements that will ensue, overall for this President it will be considered a success. His speech offered more of a vision than we have been accustomed to seeing and connected the US to its traditional allies in this struggle.

If President Trump is able to do more of this in the coming days, it is possible to see how the trip could be more effective than his critics suspect, and even provide the seeds for a more successful foreign policy ahead.

But any single speech has to be placed in context. For President Trump to succeed overseas, he needs to change much more of his style and policies than one speech can correct. Shortly before the speech, his comments during the questions-and-answers session of the joint press conference pointed to one of his biggest challenges.

He spent much of his time, in response to questions about the anti-CNN wrestling video and Russian hacking, by playing to the base. He grew defensive about the Russian intervention into the 2016 election, backing away from strong statements against Vladimir Putin and detoured into his quips about the major news networks. The striking detour was a reminder of the lack of focus that has kept this President, thus far, from moving forward with the kind of agenda he tried to articulate in his Warsaw speech.

The decision to deliver this speech in Poland, likewise, points to some of the reasons there is not broader confidence in his ability to fight against the major threats that we face. The right-wing populist government of Poland has undertaken many actions that have been roundly condemned throughout the world. The Polish government has not done enough to protect human rights, has restricted the freedom of the press, taken a hard line against admitting refugees and rejected international efforts to deal with climate change.

Many reporters might have felt unsettled about watching President Trump, standing next to the leader of a government that has been so hostile toward a free press , delivering his familiar remarks about the "fake news" media. By allying with this kind of regime, President Trump makes it more difficult to build strong support among key NATO allies who fear authoritarian movements.

Strengthening these alliances will be essential to mobilizing the kind of economic muscle needed to combat the threats that the US faces. It is also vital so that the US can maintain some kind of moral credibility if this is to be a fight to save democracy. The President must begin by standing for the most basic democratic values.

Consistency also matters. At this point, President Trump has said many things, many of which were contradictory. The reason that so many NATO leaders remained skeptical about his Rose Garden comments about Article 5 had to do with his refusal to articulate his commitment during his previous trip to Europe and his ongoing attacks on NATO since his campaign began.

Although he finally offered some tough words against Russia, his comments must be balanced with his refusal to take a stronger stand against the Russian intervention in the election or other acts of aggression that have been undertaken by Putin.

On most issues, President Trump has flipped and flopped so much that it is difficult for a speech like the one he delivered Thursday to have the same kind of resonance as other famous presidential addresses overseas -- such as when Ronald Reagan stood in front of the Brandenburg Gate 30 years ago and told Soviet leader Mikhail Gorbachev to 'tear down this wall!"

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If President Trump wants to follow through on some of the ideas in the speech, he will need support within the US that goes far beyond his electoral base. While smashing "fake news" or constantly challenging the intelligence community might be great politics in the portion of the electorate that steadfastly supports him, it is not a way to broaden his support, even within those parts of the Republican Party that have stood by him for partisan loyalty.

The costs of his political strategy have become clear with his empty legislative record. If he wants to make bold foreign policy happen, part of that task requires winning over the hearts and minds of larger parts of the American electorate than the people who like him, regardless of what he does.

Presidential speeches are extremely important and they can have lasting effects on foreign policy. But speeches are only one part of the presidential package. President Trump brings with him an enormous amount of baggage, much of which was on display just about an hour before the Warsaw address. He will have to shed it if he wants to make something more of his legacy on the international stage.