Republicans long have worried about how to survive as conservative GOP voters die off and are replaced by more liberal younger Americans.
A new national poll of millennial voters suggests that the 2016 presidential race has only hastened the shift they have feared.
The preference of voters younger than 30 for a Democrat over a Republican as the November victor nearly doubled in the last year as the presidential campaign grew in prominence, according to the survey by Harvard's Institute of Politics.
Currently 61% prefer a Democrat in the White House, and 33% favor a Republican, the poll found. In a similar survey released last spring, the gap between the two parties was only 15 percentage points.
Republican front-runner Donald Trump was far and away the least popular candidate among those polled. Overall, only 17% of millennials had a favorable view of him, and 6 in 10 said they had a "very unfavorable" view of him. Just under a quarter had a favorable view of the other two Republican candidates, Ohio Gov. John Kasich and Sen. Ted Cruz of Texas.
Among Republicans, Trump was seen negatively by 57%. Only 1 in 3 Republicans felt the same way about Cruz or Kasich.
Not surprising, Democratic front-runner Hillary Clinton swamped Trump among likely voters in a presidential matchup, 61% to 25%, despite her significant negative ratings.
Trump was losing to her in part because of a significant drop-off among young Republicans and those who had previously sided with the party's politicians.
Of those who voted for Republican Mitt Romney in the 2012 general election, only 60% favored Trump, and 13% supported Clinton. A much higher proportion of President Obama's 2012 voters — 82% — sided with Clinton, and only 5% planned to switch to the Republican.
In another measurement, young GOP voters said by a margin of 82 points that they wanted a Republican in the White House. But when asked specifically about Trump, there was a much smaller 44-point divide between those wanting him in the White House as opposed to Clinton.
"We see a good number of young Republicans telling us essentially that there's no place to go," said John Della Volpe, director of polling for the Harvard Public Opinion Project.
Clinton's continued difficulty in attracting young voters was evident in the poll. More than half — 53% — had a negative view of Clinton even as they favored Democrats generically. Only 37% had a favorable view of her, the poll found.
According to exit polls, Sen. Bernie Sanders of Vermont has consistently beaten Clinton this year among voters younger than 30, sometimes 4 to 1. She has succeeded largely by building her advantage among older voters, who are more likely to cast ballots.
Sanders was the only candidate with a net favorable impression. Fifty-four percent had a favorable view of him, compared with 31% who did not. The poll did not measure the Democratic primary race.
Although the poll found broad disdain for the GOP candidates, it also revealed problems for establishment Democrats, if they hadn't grasped that from this year's tumultuous primary season.
By 48% to 16%, young voters said politics today was not up to meeting the challenges facing the country. By 54% to 11%, they said elected officials do not have the same priorities as they do. Six in 10 said elected officials are motivated by selfishness.
Only 15% said the country was headed in the right direction, a drop of 8 points from one year ago.
When presented with a list of issues, it was clear why Sanders has caught millennials' fancy.
Just under half said that healthcare was a right — a signature line for Sanders — and that it should be paid for by the government if necessary. Only 21% disagreed.
As with healthcare, support for more government spending to reduce poverty and for measures to curb climate change — even if they cost jobs — also grew over the last year.
Della Volpe said that ideological chord is what Sanders has struck in many young voters.
"Presidential campaigns and other historic moments at times force young people to think about politics in a very different way," he said. "It's tangible in an election year."
Clinton's standing reflected a certain amount of ambivalence on the part of younger voters, particularly women.
When her competition was Trump, she fared well. In the general election matchup, women sided with her by a 42-point margin, 57% to 15%. Male voters, by contrast, backed her by a much smaller margin of 18 points. Clinton also had huge support among young African American and Latino voters when Trump was the alternative.
But when Clinton was competing with Sanders, the gender gap changed.
Asked which of the five candidates would improve women's lives more, 32% of men said Clinton, and 21% said Sanders. Women, however, gave the edge to Sanders, at 30%, over Clinton, at 26%.
When it came to whether they had a negative or positive view of the candidates, women were slightly more positive about Clinton than men were. They also saw Sanders more favorably than men did.
Men and women also had different views when it came to whether women face a glass ceiling that blocks their advancement.
Men were split, with 50% saying women faced barriers and 48% saying they did not. Among women, 68% said there was a glass ceiling, and only 30% disagreed.
After she lost the Democratic nomination to Barack Obama in 2008, Clinton bowed out by expressing pride in putting cracks in a glass ceiling. This year, in her second run, she regularly alludes to a new promise to shatter it.
The poll surveyed 3,183 Americans ages 18 to 29 from March 18 to April 3. It has a margin of error of plus or minus 2.4 percentage points.