DECORAH, Iowa — Hours after an American drone strike killed Iran’s top military commander, Joseph R. Biden Jr. stood in a barnlike building in Independence, Iowa, thundering about the importance of electing an experienced president as America faces tumult abroad — and “maybe, God forbid,” war.

About 70 miles away, Senator Bernie Sanders was just as passionate as he denounced military spending and encouraged international diplomacy.

“Maybe what we should be doing is figuring out how as a planet we work together instead of going to war with each other,” Mr. Sanders told the crowd on Friday inside a building on the Winneshiek County fairgrounds. Earlier in the day, he emphasized the need to “get our priorities right” by investing in issues at home rather than on military action abroad.

Amid signs that both Mr. Biden and Mr. Sanders have found their footing in Iowa after months of being overshadowed here, they are now aggressively seizing on the escalating tensions with Iran to press their starkly divergent cases for the presidency as they compete for an overlapping slice of the electorate.