As the struggle for control of the Senate played out in swing states across the country on Tuesday night, the Democrats were quickly assured of preserving one of their safest seats: Senator Chuck Schumer of New York, as expected, was re-elected to a fourth term — clearing the way for him to become his party’s leader in the Senate.
Mr. Schumer easily flicked away his Republican challenger, Wendy E. Long, who had eagerly embraced the outsider ethos and convention-defying policy positions of Donald J. Trump, the Republican nominee for president, riding New York’s Democratic majority and his own deep name recognition to a nearly effortless victory.
Mr. Schumer will succeed Senator Harry Reid of Nevada, who is retiring, as the chamber’s Democratic leader.
Mr. Schumer, a former congressman from Brooklyn who was first elected to the Senate in 1998, rumbled past Ms. Long, a Manhattan lawyer whose only other foray into electoral politics — as Senator Kirsten E. Gillibrand’s Republican opponent four years ago — also ended in double-digit defeat.
Confronting Mr. Schumer’s overwhelming advantage as a longtime incumbent in a heavily Democratic state, Ms. Long never came close to winning. That she ran a minimalist campaign staffed by political amateurs and sustained by only a trickle of contributions did not help. But Ms. Long had counted on a surge of support for Mr. Trump to carry her further than the average Republican candidate in New York.
In Connecticut, Senator Richard Blumenthal, the Democratic incumbent, easily beat the Republican challenger, Dan Carter, a state representative and Air Force veteran running in his first statewide election.
But in several closely watched congressional races across New York State, the backlash against Mr. Trump that Democrats had hoped would help them inch toward a House majority failed to materialize on Tuesday. In matchups in the Hudson Valley and the Binghamton area and on Long Island, voters did not punish down-ballot Republicans, as the Democrats had predicted. Instead, even as New York and its electoral votes were called for Hillary Clinton, the Democratic nominee for president, the balance between Republican-held and Democratic-held seats in the state was set to remain static.
The Democrats retained retiring Representative Steve Israel’s seat in the Third Congressional District on Long Island, where Thomas R. Suozzi, a former Nassau County executive, won by healthy margin over State Senator Jack Martins.
Mr. Suozzi’s victory was a political comeback years in the making: Once a prominent Democrat who ran against Eliot Spitzer in the 2006 primary for governor, Mr. Suozzi unexpectedly lost the Nassau County executive’s office to Edward P. Mangano, a Republican, in 2009. (Mr. Mangano was arrested and charged in a bribery scheme last month.)
Republicans held onto an open seat of their own, this one in the 19th Congressional District in the Hudson Valley. The clash there — to succeed Representative Chris Gibson, who is retiring — pitted John Faso, a Republican former state assemblyman who is well known and well liked in the district, against Zephyr Teachout, a law professor who became a liberal darling after making surprisingly strong run against Gov. Andrew M. Cuomo in the 2014 Democratic primary.
Ms. Teachout attracted the high-profile endorsement of Senator Bernie Sanders of Vermont, but by Tuesday night, Mr. Faso had been declared the victor in a close race.
In the 24th Congressional District near Syracuse, Representative John Katko, a Republican, defeated the Democratic challenger, Colleen Deacon.
And in the First Congressional District on Long Island, Representative Lee Zeldin, a Republican, rebuffed a challenge from Anna Throne-Holst, a Democrat. Mr. Katko and Mr. Zeldin had taken different tacks when it came to Mr. Trump’s candidacy. Mr. Katko, who is known as a moderate, disavowed the nominee; Mr. Zeldin, a fervent Trump supporter, ignited a controversy by suggesting that if Mr. Trump was a racist, so, too, was President Obama.
In the Binghamton area, in the 22nd Congressional District, Claudia Tenney, a Republican assemblywoman, overcame two opponents to win: Kim Myers, a Democrat, and Martin Babinec, a businessman whose independent candidacy showed strength early on but who had faded by Tuesday. While Ms. Tenney supported Mr. Trump, some of her television ads had asked voters to elect her because she would “stand up to Hillary Clinton.”