Prime Minister Benjamin Netanyahu of Israel walked into the Oval Office on the morning of Feb. 11, determined to keep the American president on the path to war.

For weeks, the United States and Israel had been secretly discussing a military offensive against Iran. But Trump administration officials had recently begun negotiating with the Iranians over the future of their nuclear program, and the Israeli leader wanted to make sure that the new diplomatic effort did not undermine the plans.

Over nearly three hours, the two leaders discussed the prospects of war and even possible dates for an attack, as well as the possibility — however unlikely — that President Trump might be able to reach a deal with Iran.

Days later, the U.S. president made clear publicly that he was skeptical of the diplomatic route, dismissing the history of negotiating with Iran as merely years of “talking and talking and talking.”

Asked by reporters if he wanted regime change in Iran, Mr. Trump said it “seems like that would be the best thing that could happen.”

Two weeks later, the president took the United States to war. He authorized a vast military bombardment in conjunction with Israel that swiftly killed the country’s supreme leader, pummeled Iranian civilian buildings and military nuclear sites, thrust the country into chaos and triggered violence across the region, leading to the deaths so far of six U.S. troops and scores of Iranian civilians. Mr. Trump has said more American casualties are likely as the United States digs in for an assault that could last weeks.