WASHINGTON — Divided, impassioned, and roiling with a mix of determination and anxiety, voters go to the polls Tuesday to decide one of the most anticipated midterm elections in recent memory.

It arrives amid a final run-up rocked by a mass shooting at a Pittsburgh synagogue, an attempted bomber who targeted President Trump's perceived enemies, and the president's vilification of a caravan of migrants in Central America, all stirring a country already heaving with unrest.

"There is no question that this is the most toxic climate in my lifetime," Rep. Brendan Boyle (D., Pa.), 41, said at a forum Monday.

In many ways, the 2018 campaigns have only amplified the tension that never seems to have abated after Trump's election.

"We've had elections where there have been high levels of voter interest and deep partisanship. We've also had elections where external events have propelled people to the polls," said Brigid Harrison, a political science professor at Montclair State University in New Jersey. "But I think that what is unique about this election is that you have both."

You'd have to look back to the 1960s for an era when political conflict mixed with violence on the recent scale, said Julian Zelizer, a political historian at Princeton University.

"It feels like the divisions of the country now are running deep and in dangerous places," he said.

After the synagogue shooting, former Pennsylvania Gov. Tom Ridge, a Republican, released a statement calling the murders "a tragic manifestation of divisive, mean and intolerant civic leadership," and worrying "about the direction our leaders are taking us."

In that atmosphere, Tuesday's election will first and foremost decide control of the U.S. House and Senate, with the outcomes determining the limits or possibilities of the next two years of Trump's presidency.

At the same time, it represents a test of the stunning results of 2016.

Did Trump's victory mark a definitive turning point in the country's attitudes and expectations of the presidency? Or an aberration brought on by a rare confluence of factors?

>> READ MORE: How President Trump is shaping the 2018 midterms

The midterm won't provide a definitive answer — Trump isn't on the ballot and many presidents have suffered midterm rebukes only to win reelection — but it will provide clues.

If Republicans keep control of Congress and minimize losses, it could affirm Trump's approach, embolden him, and again show his power to defy the conventional political wisdom with his nationalist "America First" message.

The shock of it, however, has stirred a wave of Democrats who have tried to channel their dejection into a proactive response.

"I can't fix Donald Trump. There's nothing I can do about that," said Andrea Barton Gurney, a Burlington County Democrat. "But [Rep.] Tom MacArthur, my congressional district and my local politics, they're all my responsibility."

Barton Gurney, 57, had always voted — but became a committed activist after the 2016 election, and now is working to help Democrat Andy Kim defeat MacArthur, her Republican congressman. She is emblematic of a surge of newly energized suburban women who have sparked Democratic hopes of taking the U.S. House majority.

Another, Chester County's Chrissy Houlahan, decided to run for the House after experiencing the dismay of her 26-year-old daughter, who is gay, and her father, a Holocaust survivor, following Trump's victory.

"Thousands of people that I met share that sort of anxiety, still," Houlahan said — that "the values that we have are not necessarily being represented by our leadership right now."

Houlahan, like other Democrats, stressed that she is not running only to oppose Trump — she pointed to issues such as health care, jobs, and education — but said "decency" had emerged as the "fourth issue" in her campaign. She said the bombing attempts and shooting underscored that imperative.

"There's a sense of positive resolve right now," she said in a phone interview as she counted down to the final 100 hours of the campaign. "We have been collectively energized to realize how important it is to vote, frankly."

One of many first-time candidates at the forefront of the Democratic push, Houlahan, 51, is strongly favored over Republican Greg McCauley to win a GOP-held seat nearly two years after she organized a bus ride — stocked with doughnuts, fried chicken, and red wine — to join thousands of other women who marched through Washington in response to Trump's inauguration.

The fight for the House now hinges heavily on suburban races like hers, especially in Pennsylvania and New Jersey. Democrats need a 23-seat gain to build a House majority, and see hope for gaining from four to 10 seats in the two states.

The Senate is a different picture: Most of the key races there are in more rural states where Trump has strong support, giving Republicans hope of holding or expanding their 51-49 majority.

In many ways, Zelizer said, the country is still fighting the cultural battles that erupted in the 1960s.

"One big difference is the president has totally fueled the animosity and anger in a way that presidents usually don't do," he said. "He wants to stoke the anger, and he's not doing it in subtle ways."

Trump, who has blitzed conservative areas with rallies, encapsulated his final pitch by tweeting a video that equates Hispanic migrants to one criminal's raving about killing police, and saying Democrats support such criminals. It was widely condemned, including by some Republicans, as both untrue and one of the most openly racial political appeals in recent history.

But Trump's uncompromising approach — on immigration and trade — has often galvanized his base and drawn many working-class whites to his side.

Jeff McGeary, a Trump supporter from Bucks County who has volunteered for other Republicans this year, said border security resonates with independents and blue-collar Democrats.

The only shock, he said, is "that we have a president that's actually addressing the issue head-on and folks are not used to hearing that," said McGeary, 41, a lieutenant colonel in the Army Reserve who owns a digital marketing agency. "We have to take care of our national American family first."

Trump supporters believe the president has been unfairly maligned, especially by the media, and many see this election as a chance to defend him.

Though the migrant caravan was more than 800 miles from the U.S. border late last week (farther than a walk from New York to Chicago), Trump has framed it as an existential threat in an attempt to rally his supporters.

"I'm worried about these people coming to invade. I call them the horde," Christy Vorob, 54, said recently in Scranton, where she attended a campaign stop by Trump's son Eric.

Scott Wagner, the Republican running against Gov. Wolf, is closing with an ad warning that "a dangerous caravan of illegals careens to the border."

Other GOP ads have cast Democrats as terrorist sympathizers, allies of "mobs" of black-clad protesters, or as puppets of George Soros, the liberal mega-donor, bogeyman of conspiracy theories — many of them anti-Semitic — and target of one of the pipe bombs sent last month.

Such dark warnings seem aimed at again rousing voters in conservative states, but the approach has again raised concern that it could damage Republicans in suburban areas.

Some have tried to distance themselves from Trump's message.

"Will you stand up to President Trump? The answer is yes," Bob Hugin, the Republican Senate candidate in New Jersey, said in a late television ad. His opponent, Sen. Bob Menendez (D., N.J.), has reminded voters that Hugin backed Trump as a delegate at the GOP national convention and gave $200,000 to Trump-related political committees.

A new ad for Rep. Keith Rothfus, a Republican running in a difficult race against Democratic Rep. Conor Lamb just outside Pittsburgh, shows a diverse collection of people flashing across the screen, including one man in a yarmulke, and the message "we are one nation, indivisible."

Reps. Brian Fitzpatrick, of Bucks County, and South Jersey's MacArthur have cast themselves as independents focused on local issues.

They have tried in particular to draw attention to a surging economy — a pitch that got a last-minute boost Friday with another encouraging report on jobs and wages — though Trump's relentless push on immigration has overshadowed that topic.

Polls have shown historic levels of interest in the election. At the same time, the aftershocks of the 2016 election, when so many forecasts were proven wrong, have shrouded this election in uncertainty.

Knowing how slim margins might make a lasting impact, Barton Gurney has scheduled time off work to canvass all weekend, Monday, and Tuesday in South Jersey.

She hopes to mark election night with a goofy dance she made up — she calls it "the blue wave."

Staff writers Chris Brennan, Angela Couloumbis, Holly Otterbein, Amy S. Rosenberg, and Andrew Seidman contributed to this report.