Kamala Harris and Donald J. Trump are locked in a dead heat for the popular vote, 48 percent to 48 percent, the final national poll by The New York Times and Siena College has found, as Ms. Harris struggles for an edge over Mr. Trump with an electorate that seems impossibly and immovably divided.

The result, coming less than two weeks before Election Day, and as millions of Americans have already voted, is not encouraging for Ms. Harris. In recent elections, Democrats have had an edge in the popular vote even when they have lost the Electoral College and thus the White House. They have been looking to Ms. Harris to build a strong national lead as a sign that she would do well in such critical swing states as Michigan, Pennsylvania and Wisconsin.

[Nate Cohn evaluates whether Donald Trump could win the popular vote but lose the Electoral College.]

Ms. Harris and Mr. Trump remain effectively tied even after three of the most tumultuous months in recent American political history. A high-profile debate, two attempts on Mr. Trump’s life, dozens of rallies across seven battlefield states and hundreds of millions spent on advertisements have seemingly done little to change the trajectory of the race.

Ms. Harris’s position, if anything, may have declined among likely voters since the last Times/Siena College poll, taken in early October. At the time, she had a slight lead over Mr. Trump, 49 percent to 46 percent. The change is within the margin of error, but The Times’s national polling average has registered a tightening in polls over the past few weeks as well, suggesting at the very least that this contest has drawn even closer.

[Follow the latest polls and see updated polling averages of the Harris vs. Trump matchup.]

While this latest Times/Siena College poll offers a glimpse into national sentiment, the presidential election will be decided in the seven battleground states where Ms. Harris and Mr. Trump have devoted the overwhelming amount of their time and resources. Most polls in those states — Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania, Wisconsin — suggest the contest is equally close.