Editor's Note: (Julian Zelizer, a history and public affairs professor at Princeton University and a New America fellow, 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) With the cruise missile attack on a Syrian airbase, President Trump has turned the national conversation away from the Russia scandal and White House infighting.
He now has in front of him the possibility of making progress on one of the most vexing problems in foreign policy. Unlike on many issues, much of world opinion seems to be on Trump's side. Syrian President Bashar al-Assad "carries responsibility for these developments," declared French President Francois Hollande and German Chancellor Angela Merkel in a joint statement.
But launching missiles is the just a first step. What comes next will really test the mettle of this administration as the responses from all the parties to the Syrian civil war and the larger political situation surrounding it starts to take shape. And there are many questions about whether Trump is up to the job of helping to solve Syria's crisis.
The President now faces the kind of test that confronted earlier presidents, some of whom demonstrated the ability to respond with confidence, with gravitas, and with the right mix of diplomacy and militarism.
The White House legends, like Franklin Roosevelt after Pearl Harbor in 1941 or John F. Kennedy with the Cuban Missile Crisis of 1962 or Ronald Reagan with the Intermediate-Range Nuclear Forces Treaty of 1987, demonstrated this resolve. In all of these cases the credibility of the president with the public and with international leaders was essential to their success.
President Roosevelt had demonstrated since his election in 1932 his ability to be an effective president who built a strong political coalition within the United States and who had slowly guided the nation toward a more internationalist posture despite the persistence of isolationism in Congress.
Despite the Bay of Pigs fiasco, Kennedy by 1962 had proven himself to be an intelligent and thoughtful commander in chief who displayed a strong sense of the various policy issues facing the nation and who had a steely demeanor that helped him navigate the political challenges that he faced.
When the hawkish Reagan met with Soviet Premier Mikhail Gorbachev over a series of summits, he showed the right balance of being able to concede on issues that were risky with his political base at home while maintaining a firm posture so that he could ultimately sell his historic arms agreement with our adversary to the Congress back home.
By the time of the final meeting with Gorbachev, who came to Washington ready to make a deal, Reagan had survived the Iran-Contra scandal and rebuilt public support. Politically, Reagan could still rally most of the Republican Party, and even a fair number of Democrats, when push came to shove. For leaders of other countries, this matters.
A key indicator of presidential credibility lies in whether politicians and foreign leaders believe that the commander in chief will move forward with threats and keep key promises. Adversaries and supporters need to have confidence that a president can carefully handle the difficult moments of being a leader, particularly in crises.
Other political leaders need to have some confidence that they can predict what a president will do and how he or she will act in the near future. Going into the Syria strike, Trump did not have this same kind of credibility.
The attack brings to mind some of the "Wag the Dog" questions that arose when President Bill Clinton used missiles in the middle of the Monica Lewinsky scandal, with "Wag the Dog" a reference to the film with Robert De Niro and Dustin Hoffman where an administration manufactured a war to distract attention from a scandal.
During the campaign and during the course of the First Hundred Days,Trump has repeatedly undermined his own efforts to strengthen the perception that voters and heads of other nations have about his presidency.
Thus far, he has run a presidency aimed to appeal primarily to his base of supporters. His actions and statements have done almost nothing, as is evident through his historically low approval polls, to give others confidence in his ability to deliver.
The constant tweet storms attacking his opponents have created the impression of a president who in the early morning hours is out of control and willing to make provocative, and false, statements without consideration of the consequences. He has repeatedly threatened his adversaries, including China, without actually following through on his remarks.
With Syria, there are doubts about whether Trump has any kind of a long-term plan other than to be reactive. After the strikes, strong and thoughtful diplomatic moves will be essential to making sure this does not disintegrate into even more brutal violence.
As a former Obama administration official, Antony Blinken, wrote in The New York Times, the administration "must prevent or mitigate the possible unintended consequences of using force, including complicating the military campaign against the Islamic State. All this will require something in which the administration has shown little interest: smart diplomacy."
He will also need to build a durable base of political support for whatever steps he takes. The failure of health care reform, and the empty legislative basket from his Hundred Days suggest that he doesn't really have the ability to move members of Congress on issues that he considers to be urgent.
The failure to staff key agencies like State Department and the laggard manner in which Trump handled the transition period suggests that this is a president whose own executive branch is not even all ready to go. And the ongoing scandal over Russia's role in the 2016 election has left a massive dark cloud hovering over the White House.
All of these problems add up. Heads of state and the leaders of terrorist organizations are no doubt thinking about how President Trump will handle these difficult situations. Foreign leaders will ask how much they can trust him to deal with crises and negotiations with the kind of caution and poise that international relations require. They will wonder whether they should take seriously his threats -- from economic sanctions to military action.
President Trump likes to think that he is his own man and that he can continue to do things the way he wants to without listening to the so-called establishment whose rules and norms he finds to be irrelevant.
That might work in the realm of reality television but it's a dangerous path when it comes to international relations and national security. The President needs to have a certain amount of credibility — credibility that he can handle tough situations without causing more chaos, credibility that he has a strong base of political support that will allow him to gain the backing he needs when taking on controversial matters and the credibility to deliver on the threats and promises that he issues when engaging with the world.
Trump needs to address his credibility challenges to make progress in Syria and to further US interests around the world.