Defying almost all forecasts, Donald J. Trump won the presidential election early Wednesday morning, an outcome that surprised most of the nation. After a long night of watching and waiting, Mr. Trump finally achieved the 270 electoral votes needed to win at around 3:30 a.m.

Almost all major news sources and pollsters predicted a win for Hillary Clinton entering Election Day, but the race quickly changed, as soon as results began coming in and especially when votes were tabulated in the so-called “Rust Belt” states.

Mr. Trump racked up an early lead and then the mood shifted at both his election headquarters and Mrs. Clinton’s, each located in New York City, as the Republican won swing state after swing state.

Mrs. Clinton was never very far behind, but she was unable to take a lead and her team could only watch in frustration as she lost a succession of narrow races.

“Donald Trump is going to be our president; we owe him an open mind and a chance to lead,” Mrs. Clinton said Wednesday in her concession speech. Clearly emotional, it likely marked Mrs. Clinton’s final run for public office and denied her the historical distinction of being the nation’s first female president.

Everything that could go wrong for her seemingly did. The major swing states, such as Florida, Ohio, Michigan, Pennsylvania, Nevada, and New Hampshire, were all decided in excruciatingly close fashion. Some dragged on until the morning hours, long after the polls closed.

To the shock of many, Mr. Trump was able to navigate an extremely narrow path to victory, winning all of the big swing states and taking three from Mrs. Clinton’s column that were unexpected: Pennsylvania, Michigan, and Wisconsin.

As the night went on, it was ironically her path that became more and more narrow, until it eventually just wasn’t there at all.

“I pledge to every citizen of our land that I will be president for all Americans, and that’s so important to me,” Mr. Trump said in his victory speech, also on Wednesday. “Every single American will have the opportunity to realize his or her fullest potential.”

The popular vote, when it is made official, will go to Mrs. Clinton, probably by a single percentage point. It is the fifth time, and the second in 16 years, that the Electoral College tally and the popular vote will diverge.

The election has left the nation divided on many issues, which is why there have been repeated calls for unity in the aftermath. Bridging that divide is a steep challenge for any incoming president.

“Everybody is sad when their side loses an election, but the day after we have to remember that we’re actually all on one team,” President Barack Obama said Wednesday. “We’re not Democrats first, we’re not Republicans first, we’re Americans first.”