NEW DELHI — Only one month ago, Narendra Modi, India’s once unstoppable prime minister, seemed surprisingly vulnerable going into his re-election campaign.

Economic growth had been slowing, thousands of farmers were marching on the capital (some even dumped gallons of nearly worthless milk in the streets), and unemployment had hit its worst level in 45 years — an unpleasant fact that Mr. Modi’s government tried to hide.

In a recent batch of critical state elections, his party got trounced. And with the country’s weekslong election process set to begin on April 11, the rejuvenated opposition was landing punch after punch with corruption allegations.

But one bombing in Kashmir, and weeks of military brinkmanship with Pakistan afterward, appears to have interrupted Mr. Modi’s slump.

But after the crisis with Pakistan, the conversation on many farms has changed, said Vijay Jawandhia, a farmer and leader of a farmers’ union from Maharashtra State.

“I hear farmers saying he is more decisive,” he said.

According to Gilles Verniers, an assistant professor of political science at Ashoka University, near New Delhi, 40 percent of India’s 900 million voters typically remain undecided until right before the election. Unlike with politics in the United States, where people tend to pick a party and stick with it, many voters in India tack back and forth between the major parties depending on the candidates and the issues of the day.

Mr. Verniers said the crisis with Pakistan was certain to “tame the decline” Mr. Modi had been facing.

Before the attack in Kashmir, a disputed territory that both India and Pakistan claim, Mr. Gandhi, the leader of the Congress party and the scion of a storied political dynasty, had gained a new spring in his step. He was speaking out forcefully about a murky jet fighter deal that Mr. Modi’s government made with France, and he enlisted his popular younger sister, Priyanka, to join the campaign, delivering it a jolt of energy.

Both Congress and the B.J.P. have struck alliances with regional parties in the hopes of forming a governing coalition. The biggest leftist parties, including communists and those dominated by lower castes, are likely to back Congress, while some of the largest parties in Punjab and Maharashtra, two populous states, are firmly on Mr. Modi’s side.