WASHINGTON — Donald J. Trump, exuding confidence after his resounding primary victories in the East, promised a foreign policy on Wednesday that he said would put "America first." He castigated President Barack Obama and Hillary Clinton, a former secretary of state and a possible opponent in the general election, for what he described as a string of missteps that have disillusioned the nation's allies and emboldened its rivals.
Trump, the front-runner for the Republican presidential nomination, pledged a major buildup of the military, the swift destruction of the Islamic State and the rejection of trade deals that he said tied the nation's hands. But he also pointedly rejected the nation-building of the George W. Bush administration, reminding his audience that he had opposed the Iraq War.
"America is going to be strong again; America is going to be great again; it's going to be a friend again," Trump said. "We're going to finally have a coherent foreign policy, based on American interests and the shared interests of our allies."
"The world must know that we do not go abroad in search of enemies, that we are always happy when old enemies become friends and when old friends become allies," he added. "That's what we want: We want to bring peace to the world."
For Trump, whose campaign appearances are often a gleeful exercise in showmanship and off-the-cuff wisecracks, the speech had all the trappings of a serious address. Standing beneath a twinkling chandelier in a Washington hotel ballroom, backed by American flags and facing a sedate, largely gray-haired audience, a measured Trump read his remarks from a teleprompter, staying almost completely on script.
But if Trump adopted establishment trappings, his speech still had an insurgent tone. He criticized allies in Europe and Asia for not bearing the burden of their own defense, he said he would try to mend fences with Russia, and he assailed his opponents for being overly aggressive in foreign affairs. Trump said he had no plans to take advice from the foreign policy elite, and his agenda reflected that — a mélange of ideas that defied Republican and Democratic orthodoxy.
There were paradoxes throughout Trump's speech. He called for a return to the coherence of U.S. foreign policy during the Cold War. Yet he was openly suspicious of the institutions that undergirded that era. He promised to eradicate the Islamic State, but said the campaign against extremism — or as he called it, "radical Islam" — was as much a philosophical struggle as a military one.
"Our friends and enemies must know that if I draw a line in the sand, I will enforce that line in the sand — believe me," Trump said. "However, unlike other candidates for the presidency, foreign aggression will not be my first instinct." He did not mention anyone by name, though his strongest Republican opponent, Sen. Ted Cruz of Texas, has threatened to carpet-bomb the Islamic State until the desert sand glows.
Trump's speech drew negative reaction across the political spectrum. Sen. Lindsey Graham, R-S.C., posted on Twitter that "Ronald Reagan must be rolling over in his grave." Lanhee Chen, a fellow at the Hoover Institution who advised Mitt Romney, the 2012 Republican nominee, said "There was clearly an isolationist strain to the speech, but that runs into the reality of the world that we live in."
R. Nicholas Burns, a former senior State Department official under Bush who now advises Clinton, said, "He's casting these thunderbolts and threats at our allies, and yet there was almost a kid-glove treatment of Russia and China."
Even Trump's embrace of the slogan "America first" raised eyebrows, with critics noting that it was popularized in the 1930s by aviator Charles A. Lindbergh and other isolationists who opposed the United States' entering World War II. "To fly the banner of America First shows that he has historical amnesia or just doesn't understand history," Burns said.
In one of his few concrete proposals, Trump said he would convene summit meetings in Europe and Asia to overhaul NATO and rebalance nuclear security arrangements with Japan and South Korea. He did not repeat a statement he made to The New York Times that those countries should consider acquiring their own nuclear weapons.
Trump was scathing about the Obama administration's intervention in Libya, lashing Clinton to the policy, which he said had left a security vacuum filled by the Islamic State. He also faulted Obama for his failure to enforce the red line he laid down in Syria. Yet Trump made clear he would use military force only as a last resort.
"We're getting out of the nation-building business and instead focusing on creating stability on the world," Trump said.
On pressing issues like counterterrorism, Trump broke little new ground. He declined, for example, to give any details on how he planned to destroy the Islamic State to avoid tipping the military's hand, beyond vowing that "they will be gone quickly."
Trump repeated his desire to seek improved relations with Russia and its president, Vladimir V. Putin — a strategy that carried echoes of Obama's attempt to "reset" relations with Russia after its invasion of Georgia in 2008. But he said his skills as a deal-maker would make him more successful at it.
"I see improved relations with Russia, from a position of strength, as possible," Trump said. "Some say the Russians won't be reasonable; I intend to find out."
In another echo of Obama, Trump said he would seek advice from outside the foreign policy establishment. He said he would choose "the best minds" with practical solutions, rather than people with "perfect résumés" and records of failure around the world. He did not mention any names.
Trump promised to make the United States more dependable in the eye of its friends and allies, and more respected by its enemies. Yet just moments earlier, he also advocated increased unpredictability. "We have to be unpredictable," he said. "And we have to be unpredictable starting now."
The relatively small, invitation-only crowd consisted of journalists (seated in the back), and seven rows of guests — a largely inside-the-Beltway crowd that included Sen. Jeff Sessions of Alabama, a senior policy adviser to the campaign; a handful of House members; and Grover Norquist, the president of Americans for Tax Reform.
Trump recently overhauled his campaign team, bringing in new advisers who have begun to impose discipline and organization to what was often a chaotic campaign. The candidate himself has taken steps toward "more presidential" behavior, as he calls it.
Trump, who delights in mocking scripted candidates who use teleprompters, delivered his speech with the help of two teleprompters, and aides said he had practiced with them over the weekend. The New York billionaire worked on his foreign policy speech for more than a week, according to an aide, with the help of some advisers his campaign would not identify.
"The speech is his words and his thoughts," said Paul Manafort, Trump's newly installed campaign chief.
Trump was introduced by Zalmay Khalilzad, an Afghan-born diplomat who was Bush's ambassador to Afghanistan and Iraq, and is closely identified with the U.S. wars in those countries. Khalilzad said afterward that he was not advising Trump formally or informally, and that the two men met for the first time in a holding room adjacent to where he delivered his speech.