Representative Hakeem Jeffries convinced Jared Moskowitz to stay in his Florida race back in May. Jeffries told him, "You're the only one who can win that seat." The plan worked on Tuesday as Moskowitz won his expensive contest, helping other Democrats hold their districts despite tough pressure from the Republicans.

Back in May, Representative Hakeem Jeffries, Democrat of New York and the minority leader, saw a crucial piece of his strategy for winning control of the House slipping away.

Republicans, spurred on by President Trump, had redrawn congressional districts in Florida to favor themselves, and Representative Jared Moskowitz, a centrist Democrat from Coral Springs, was thinking of quitting rather than fighting for a third term in a far more conservative district.

Death threats were already jamming up his voice mail, and Mr. Moskowitz was frightened of what would happen to his family as Republicans trained their attacks on him.

Mr. Jeffries would not hear of it. In calls and meetings, he leaned hard on Mr. Moskowitz to stay in the race, telling him he was the key to a play to hold on to all four Democratic districts that Republicans in the state had carved up to protect the G.O.P. majority.

"You're the only one who can win that seat," Mr. Jeffries told him, promising to match the torrent of Republican money that would be spent against him. "You're the linchpin for the other three."

On Tuesday, the plan worked. Mr. Moskowitz won one of the most expensive races in the country, and the three other Florida Democrats who were under threat held on or were ahead in ballot counting.

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