But the haul is meager. On the other end, Bashar al-Assad is still in power in Syria, as is Robert Mugabe in Zimbabwe — despite more than a decade’s worth of economic sanctions by the United States and the European Union. Then there is the tale of Cuba, in which a half-century embargo has failed to bring about regime change in a tiny, economically fragile country only 100 miles off the coast of Florida.

Sanctions have proved powerless to push Turkey out of Cyprus; to move Colombia, Venezuela or Nigeria to comply with Washington’s war on drugs; to persuade India or Pakistan to abandon their nuclear arsenals.

Even the ostensible “successes” of sanctions should be scrutinized with some skepticism. Supporters like to argue that sanctions were instrumental in bringing Iran to the negotiating table. Even if sanctions imposed by President Barack Obama in 2014 did not compel Russia to leave Crimea, they add, without them Mr. Putin might have felt emboldened to send Russian forces across the Baltic republics.

And yet one could argue that Mr. Putin hasn’t moved on the Baltics because they are not as critical to Russia as Ukraine, a country through which it pumps 80 percent of the natural gas it sells to Western Europe; which was home to its Black Sea fleet before the move on Crimea; and which was flirting with moving out of the Russian orbit into the hostile arms of NATO.

Crediting sanctions with bringing Iran to the negotiating table also overlooks Iran’s choices. Leaders in Tehran knew that if the country developed a nuclear weapon, it faced a decent chance of a military strike by Israel, the United States or both. Coming to the negotiating table would not forestall its nuclear ambitions forever. And it might actually set the stage for what could prove to be a productive relationship with Washington.