ROME — Matteo Salvini’s hardline approach to a Dutch migrant vessel’s efforts to storm an Italian port has done nothing but raise his capital in the eyes of the Italian people, who elected him to curb illegal immigration.

Rado Fonda, director of leading Italian market research agency SWG, noted Friday that just one month after the European elections Mr. Salvini’s Lega party has risen by an impressive 3 percent among Italian voters, from 34 percent to 37 percent, widening its lead over the second-place Democratic Party (PD), which has remained stable at 22.6 percent.

“Matteo Salvini still has a pool of potential expansion and having gone from 34 to over 37 percent in one month he could easily reach 40 percent,” Mr. Fonda said.

The PD, on the other hand, “does not have the drive to move from being an opposition party to a governing party,” Fonda said. “The PD has regained the left-wing electorate, which had escaped into abstentionism or even the Five Star Movement, but has lost support among the moderates. It is more left, less center.”

Mr. Salvini has stood his ground in the face of international pressure to disembark 42 migrants aboard the Sea-Watch 3, an NGO vessel flying a Dutch flag, insisting that he does not give in to strong-arm tactics.

“It is clear that a German NGO vessel flying a Dutch flag, which picks up immigrants in Libyan waters and does not go to Tunisia or to Malta, but heads straight for Italy, disobeying the finance police, the Government, the Navy, everyone, does so for reasons of a political battle,” Mr. Salvini said on Twitter.

“Anyone who crashes a checkpoint with his car is stopped,” he added. “I hope that in the coming hours there will be a judge to rule that there are outlaws aboard that ship, starting with the captain.”

“If the ship is seized and the crew arrested, I will be delighted,” he said.

The interior minister also took advantage of the situation to remind Italians that his firmness in dealing with illegal immigration has saved numerous lives.

“More than 5,000 people died at sea in 2016,” Salvini noted. “This year we are at a tenth of that. We have gone from 76,858 landings in 2017 to 2,544 this year.”

“I want to continue positive trend,” he said.

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