High stakes were matched by some of President Trump's harshest campaign rhetoric yet at a rally in Fayetteville, N.C., on Monday night, with just hours to go until voters there head to the polls in a pivotal toss-up special election that will decide the winner of a long-contested -- and long-vacant -- House seat.

"To stop the far-left, you must vote in tomorrow's special election," Trump told attendees, before slamming Democratic candidate Dan McCready as a dangerous proponent of "sanctuary cities" and rolling back gun rights.

"Just recently, Mecklenburg County set free an illegal alien charged with first-degree rape and crimes against a child," Trump said, his voice rising. "Support for sanctuary cities is disloyalty to American cities -- and McCready wants sanctuary cities, with all of their protections for people who are serious criminals. Tomorrow is your chance to send a clear message to the America-hating left."

A sustained chant of "build that wall" broke out. "We don't want dangerous criminal aliens roaming free in North Carolina," Trump responded. "Our Republican candidate, Dan Bishop, will fight with everything he has."

As Bishop took the podium to speak briefly during the rally, an attendee required medical attention, leading Trump to step in and halt the event for several minutes. "Doing better?" Trump asked. "Good. I guess Dan's speech wasn't so good. Thank you, doctor. Thank you, law enforcement."

Bishop then urged attendees to pray for the individual, "because that's what we do. We pray."

Trump separately criticized Democratic presidential candidates for saying at a recent primary debate that they would give away taxpayer-funded healthcare to illegal immigrants. The Democratic field is so radical, Trump suggested, that Americans essentially have "no choice" but to vote to re-elect him.

The president also addressed the nation's progress in reducing opioid deaths, as well as his positive economic numbers, noting that "more than 7 million Americans have been lifted off of food stamps" and "nearly 600,000 Americans entered the labor force last month alone."

"The unemployment rate for African-Americans just reached another brand-new all-time low in the history of our country," Trump said to applause. "And by the way, African American-youth unemployment has also reached the lowest level ever recorded in history."

After chants of "four more years!" died down, Trump added: "The labor force participation rate for women is at the highest level now in 15 years, and soon will be 35 years, and soon, I promise, will probably end up being better than ever."

Trump also touted the nearly 200 federal judges he has successfully appointed -- including Associate Justice on the Supreme Court Brett Kavanaugh, whom Trump said was "put through hell."

"Tomorrow is your chance to send a clear message to the America-hating left." — President Trump

The president enjoys wide popularity within the Republican Party, but a GOP defeat in the red-leaning state on Tuesday could suggest trouble for his reelection campaign. State officials ordered the special election earlier this year, and invalidated a win by GOP candidate Mark Harris in the 2018 midterms, after uncovering alleged ballot fraud efforts.

Before leaving Washington, Trump dismissed questions of whether a poor result for the Republican candidate would serve as a warning sign for 2020.

"No, I don't see it as a bellwether," Trump said.

Some analysts have said the fraud scandal could undercut Bishop, and undermine any attempts to draw larger lessons from the race in the state's 9th Congressional District.

However, the special election could offer clues about the mindset of Republicans in the suburbs, whose flight from the party fueled the GOP's 2018 House election losses.

The House district flows eastward from the prosperous Charlotte suburbs into rural areas hugging the South Carolina border. State officials invalidated last November's election following allegations of voter fraud by a GOP operative.

NORTH CAROLINA POLITICAL OPERATIVE FACES MORE CHARGES IN BALLOT FRAUD CASE

The district has been held by the GOP since 1963. In 2016, Trump won the district by 11 percentage points. Should Bishop defeat Democrat Dan McCready, it could give Trump room to assert that he pulled Bishop over the top. If McCready prevails or Bishop wins by a whisker, it will suggest GOP erosion and raise questions about Trump's and his party's viability for 2020.

"This will tell us if Trump can carry candidates through suburban districts or not," said Sarah Chamberlain, president of the Republican Main Street Partnership, which represents moderate Republicans. If not, she said, the GOP must "work harder to address the concerns of suburban individuals, mainly women."

Trump also praised North Carolina Sen. Thom Tillis, who is up for re-election in 2020, and Rep. Greg Murphy, who is also up for special election on Tuesday in a solidly Republican district.

Sen. Lindsey Graham, a rival-turned-ally to the president, was also in attendance. Trump led ovations Graham as well as House Majority Leader Kevin McCarthy, Reps. David Roser, Jim Jordan, Devin Nunes, and Mark Meadows, lieutenant governor Dan Forest, and others.

Fox News personalities Diamond and Silk also received special mention as "incredible" individuals.

The rally was held just over 100 miles from the site of a Trump rally in July where "send her back" chants aimed at a Somali-born American congresswoman rattled the Republican Party. Trump later condemned the chant, which has not been repeated at subsequent Trump events.

Marshville residents Philip and Diane Ezzell, both 70, were near the front of the line Monday waiting to enter the Trump rally. Both attributed their support for Bishop to his backing by Trump.

"We like his values, and he supports Trump," Diane Ezzell said. "And we don't want no socialist clowns."

That was a reference to a TV spot by Bishop superimposing the faces of McCready and other prominent Democrats on swaying clown figures.

Cynthia Brown, of Fayetteville, 50, is also attending the rally. Brown, who is black, said supporting Trump has been "a pretty lonely experience" for her. She added, "But that's OK. I'm not a follower."

While the stakes for the House are high, Trump's trademark rallies inevitably become more about him than the local candidate, as he uses the stage to settle political scores, sharpen attacks and take on perceived foes. After a light rally schedule of late, the president will have plenty of new material to work with.

Chief among them are the White House's worries about the impact an economic downturn could have on a president who has made a strong economy his central argument for a second term. Trump advisers worry that moderate Republican and independent voters who have been willing to give him a pass on some of his incendiary policies and rhetoric would blame him — and, in particular, his trade war with China — for slowing down the economy.

WATCH: BISHOP TALKS TO FOX NEWS ABOUT THE UPCOMING ELECTION

In the hours before Monday's rally, Trump flew to coastal North Carolina to inspect the damage left by Hurricane Dorian, but bad weather forced officials to scrap those plans. Instead, he received a briefing on Air Force One where Democratic Gov. Roy Cooper told him that three deaths are connected to the storm and that some 3,500 people are without power.

At the rally, Trump praised nongovernmental organizations and agencies that have worked to help storm recovery efforts, in North Carolina and elsewhere.

McCready has not had any public events in the district with Democratic presidential hopefuls, though any such appearances by candidates jostling to appeal to liberal voters might not have helped him in the moderate area.

But former Vice President Joe Biden and Sen. Elizabeth Warren, D-Mass., two rival candidates, have emailed fundraising solicitations on his behalf. Meanwhile, Vice President Mike Pence will also campaign in the district on Monday for the Republican.

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Democrats captured 39 GOP-held House districts in the 2018 midterm elections, more than enough to give them majority control of the chamber.

Much of that turnover occurred in suburbs, largely in Democratic strongholds like California and New Jersey but also in red-leaning communities near places like Dallas, Oklahoma City and Atlanta. GOP alarm bells have been ringing about the suburbs ever since.

Fox News' Paul Steinhauser and The Associated Press contributed to this report.