WASHINGTON — As the most caustic campaign in modern American history nears its close, Hillary Clinton has built a formidable lead over Donald Trump approaching 10 percentage points, a USA TODAY/Suffolk University Poll finds. But she faces a deeply divided nation that is alarmed about the prospect of Election Day violence and what may be ahead.

A 51% majority of likely voters express at least some concern about the possibility of violence on Election Day; one in five are "very concerned." Three of four say they have confidence that the United States will have the peaceful transfer of power that has marked American democracy for more than 200 years, but just 40% say they are "very confident" about that.

More than four in 10 of Trump supporters say they won't recognize the legitimacy of Clinton as president, if she prevails, because they say she wouldn't have won fair and square.

"I have no idea who is rigging it, (but) there's just too many inconsistencies coming from all directions," says William Lister, 71, a Pittsburgh Democrat who is voting Republican for the first time to support Trump. He was among those polled. His advice: "I think everyone should vote on paper ballots this year."

Clinton supporters overwhelmingly reject the idea that the vote count can't be trusted. "It's 2016, and to be able to rig an election would be impossible at this point," scoffs Jennifer Neugebauer, 36, an orthodontic technician from Philadelphia and a Clinton enthusiast since her first presidential bid eight years ago.

"I don't think it's so much rigged against him," says Zachery Prickett, 21, of Delavan, Wis., who is supporting Jill Stein of the Green Party. "I think he destroyed his own campaign at this point."

The paradox for Clinton is that she is amassing a solid lead even as unprecedented challenges that could make governing more difficult come into sharp relief.

She now leads Trump among likely voters by 47%-38% in a four-way race. (Without rounding, she leads by 9.80 points, 47.40%-37.60%.) Support for third-party candidates has been cut in half since late August, a trend that is common for as voting nears. Libertarian Gary Johnson has dropped to 4% and Stein to 2%.

In a two-way race, Clinton leads Trump by 49%-39%.

The poll of 1,000 likely voters, taken Thursday through Monday by landline and cellphone, has a margin of error of plus or minus 3 percentage points.

If her lead holds up until the results are tallied on Nov. 8 — no sure thing — Clinton would carry the White House by the widest margin in the popular vote of any candidate since Ronald Reagan's 49-state landslide in 1984.

That said, the mood of the electorate is nothing like the optimism of three decades ago, when Reagan's gauzy re-election theme was "Morning in America."

"Since the polls are starting to shift quite a bit towards Hillary Clinton, I've been buying a lot more ammunition," says Rick Darling, 69, an engineer from Harrison Township, in Michigan's Detroit suburbs. In a follow-up phone interview after being surveyed, the Trump supporter said he fears progressives will want to "declare martial law and take our guns away" after the election.

"You can say I'm wearing my tin-foil hat," Darling says. "I don't know what's going to happen. It's so unpredictable. The country is so divided. I'm going to be prepared. If it all falls apart, I'm going to be ready if I have to be. I'm going to be a good Boy Scout."