President Biden could very well go down in history as the last American president born during World War II and shaped by a view of American power nurtured in the Cold War. No other leader on the world stage today can boast that they sat in the Israeli prime minister’s office 50 years ago with Golda Meir, or discussed dismantling Soviet nuclear weapons with Mikhail Gorbachev.
So perhaps it is no surprise that the twin wars in which Mr. Biden has chosen to insert the United States — defending Ukraine as it tries to repel a nuclear-armed invader, and now promising aid to Israel in wiping out the leadership of Hamas — have brought out a passion, emotion and a clarity that is usually missing from the president’s ordinarily flat and meandering speeches.
It rang out on Thursday evening, as Mr. Biden combined the two struggles in his Oval Office address, declaring that while President Vladimir V. Putin of Russia and Hamas “represent different threats,” they “both want to completely annihilate a neighboring democracy.”
Throughout the speech, Mr. Biden toggled between the two crises, making the case that if America does not stand up in both conflicts the result will be “more chaos and death and more destruction.” That argument reflects his certainty that this is the moment he has trained for his entire political career, a point he often makes when challenged about his age.
His sense of mission explains why, at age 80, he has in the past eight months visited two countries in the midst of active wars. But at the same time he has married his public embraces with private cautions to American allies, while carefully keeping American troops out of both conflicts — so far. He seems determined to prove that for all the critiques that the United States is a divided, declining power, it remains the only nation that can mold events in a world of unpredictable mayhem.
“When presidents get into their sweet spot you usually see and hear it, and in the past few weeks you have seen and heard it,” said Michael Beschloss, the historian and author of “Presidents of War,” which traces the rocky history of Mr. Biden’s predecessors as they plunged into global conflicts, avoided a few, and sometimes came to regret their choices.
Whether Mr. Biden can bring the American population along, however, is a more unsettled question than at any moment in his presidency, and was the backdrop of his Oval Office address.
Polls show that a growing number of Americans are uneasy with the role of defender of the existing order, and the existing rules, that Mr. Biden describes as the essence of America. In the generation in which he grew up, his Thursday declaration that “American leadership is what holds the world together” would have been uncontroversial. Today it is a central point of debate, along with his insistence that “American alliances are what keep us, America, safe.”
For Mr. Biden, the democratic order is at risk if the rest of the world balks at toppling Hamas and neutralizing Russia. But he is finding that a far harder case to make now than in February 2022, when Mr. Putin tried a lightning-strike attack to overthrow an imperfect democracy in Ukraine and restore the Russian empire of Peter the Great.
The initial overwhelming support for Ukraine — one of the few issues that seemed to unify Democrats and Republicans — is clearly shattering, with a growing part of the Republican Party arguing that this is not America’s fight. The slog across the Donbas, and the prospect of a long conflict in which Mr. Putin is waiting to see if America will elect former President Donald J. Trump or someone of similar antipathy to the war effort, only complicates the picture.