With the supposed cease-fire in eastern Ukraine a mirage, the White House can soon be expected to return to its public pondering of whether to supply Kiev’s military with lethal aid to fend off the Russian-backed insurgency. If President Obama finally does decide to send antitank weapons and other hardware the Ukrainians have pleaded for, it will be only the latest example of the administration’s too-little-too-late temporizing.

Indecisiveness is the predominant characteristic of how Mr. Obama executes U.S. national-security policy. Undoubtedly there are other influences: ideological blinders; mistrust of America’s presence in the world; inadequate interest, knowledge, focus and resolve. But in implementing his policies, good or bad, the president has shown that equivocating is what he does best.

Mr. Obama’s approach is the polar opposite of the “energy in the executive” that Alexander Hamilton advocated in Federalist No. 70, especially in foreign policy. The unitary presidency, not Congress, possesses “decision, activity, secrecy and dispatch” so necessary for high statecraft. This president’s record of dithering is long and depressing.

In June 2009 Mahmoud Ahmadinejad ‘s rigged presidential election in Iran spurred massive, peaceful protests. For several days Mr. Obama declined to address the ayatollahs’ unleashing of the Basiji militia against innocent civilians, prompting dissenters to make signs asking, “Are you with us or against us?” The Revolutionary Guards were certainly against them—and the Green Movement was brutally repressed. By the time Mr. Obama finally spoke out, haltingly, the moment had passed, and the Islamic Revolution had stabilized.

Similar hesitation applies to Mr. Obama’s handling of Tehran’s nuclear-weapons program. He has relied on negotiations and sanctions to transform Iran’s weapons infrastructure into a “peaceful” program, but this approach has consistently failed. To be effective, sanctions must be comprehensive (targeting only named individuals or firms is easily circumvented); universally accepted (not true here, as China and Russia repeatedly demonstrate); and vigorously enforced. The Obama administration’s episodic, negligently enforced Iran sanctions meet none of these tests.

President Obama chronically disregards the integral relationship between diplomacy and force. His foreign-policy mantra that “all options are on the table” regarding Iran proves the point. What from some presidents might sound ominous, from Mr. Obama sounds pro forma.

Colin Powell as secretary of state once advised British Foreign Secretary Jack Straw that “if you want to bring the Iranians around, you have to hold an ax over their heads.” Instead, Mr. Obama is holding a selfie stick over his own. The U.S. has done too little on Iran, and now we are nearly too late to stop the world’s leading state sponsor of terrorism from acquiring nuclear weapons.

Regarding North Korea’s nuclear program, Mr. Obama hasn’t acted at all. Pyongyang has had six years to advance its nuclear program and ballistic-missile efforts. In recent months U.S. and South Korean commanders have voiced fears that North Korea is near to miniaturizing its weapons and mounting them on ICBMs capable of reaching the U.S. West Coast.

In Syria, whatever slim chance there was of empowering a “moderate” anti-Assad opposition when the civil war began four years ago disappeared while Mr. Obama dithered. His declaration of a “red line” regarding Bashar Assad ‘s use of chemical weapons in Syria might have been a sign of forceful policy; it quickly faded.

In Iraq, the president’s inability or unwillingness to reach a “status of forces” agreement resulted in the 2011 withdrawal of U.S. forces, thereby leading directly to increased Iranian influence in Baghdad. The Islamic State terrorist hordes rose almost inexorably from the ashes of al Qaeda in Iraq, and its increasing control over vast portions of Syria and Iraq followed. Today, Mr. Obama’s feeble proposed authorization for military force against Islamic State should top the list of prime too-little-too-late exhibits.

Libya’s collapse after the fall of Moammar Gadhafi and the Sept. 11, 2012, terrorist attack on the U.S. consulate in Benghazi further show Mr. Obama’s unwillingness to see the growing radical-Islamist threat. He didn’t handle the threat adequately before the consulate attack, didn’t act decisively during the attack and, most egregiously, failed to retaliate or exact retribution afterward. Yemen’s current disintegration is a tragic reprise of the Libya debacle.

Mr. Obama’s sanctions-focused response to Russian aggression in Ukraine has been similarly piecemeal and ineffective. Authoritarian regimes are not impressed by hardships imposed on mere citizens; the real peril to Vladimir Putin comes from collapsing global oil prices. If the U.S. had supplied weapons to Ukraine early, it might have deterred Moscow’s aggressiveness, preventing or minimizing the conflict, thereby avoiding the slow-motion partition of Ukraine now under way. Today is too late.

Note also that the leader of the West has been absent from negotiations over Ukraine’s fate. Instead, Germany’s Chancellor Angela Merkel has the initiative—ruling out military aid, seeking a deal with Russia—largely because she assesses accurately that Mr. Obama will do nothing consequential to constrain Moscow.

Nowhere is Ukraine more closely watched than in Beijing, where Mr. Obama’s weakness and irresolution are empowering China to make ever-broader territorial claims in the East and South Seas, to suppress dissent in Hong Kong and to turn a covetous eye on Taiwan. Beijing is surely calculating that as U.S. leadership falters in Europe, so it will in the Pacific.

Why is Mr. Obama unwilling to act swiftly and decisively in foreign affairs? The most basic reason is his deterministic view of an “arc of history” bending inevitably to outcomes he finds ideologically desirable. And since a critical element of his ideology is that America’s presence in the world contributes to problems as much as solving them, the president’s policy of withdrawal and passivity is no surprise.

Failing to act when it could make a difference only feeds the appetites of aggressors. Europe acquiesced as Hitler reoccupied the Rhineland, undertook Anschluss with Austria, annexed the Sudetenland and subsequently destroyed Czechoslovakia. When Poland’s turn came, these prior hesitations had convinced Hitler that he enjoyed impunity. He told his generals weeks before invading: “Our enemies are little worms. I saw them at Munich.” Imagine what our adversaries today think of us.

Mr. Bolton is a senior fellow at the American Enterprise Institute and the author of “Surrender Is Not an Option: Defending America at the United Nations and Abroad” (Simon & Schuster, 2007). This article was originally published by The Wall Street Journal.

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