Everything you need to know about Tuesday's Arizona special election for Congress

It has been decades since Phoenix's western suburbs have seen a congressional election with any real suspense.

Since 1977, only two people — Bob Stump and Trent Franks — have represented the area in the U.S. House of Representatives. Because of the 8th Congressional District's reputation as a Republican stronghold, Democrats haven't even bothered to put a candidate on the ballot since 2012.

On Tuesday, voting ends in the special election to replace Franks, the veteran House Republican who resigned in December amid a sexual-misconduct scandal. Republican Debbie Lesko is the favorite to replace him because of her party's 17-percentage-point registration advantage in the district.

But at a time when independents, and even some Republicans, nationally are increasingly wary of the GOP, Democrat Hiral Tipirneni has mounted a serious challenge to Lesko.

How close is the race? Recent polls show anything from Lesko winning by 10 percentage points to Tipirneni by 1.

ARIZONA ELECTION LIVE UPDATES: Voting lines move quickly | Vote totals

The parties and campaigns are dissecting pictures in an effort to gain the upper hand.

Democrats point to photos of Tipirneni drawing hundreds to an event in Sun City, traditionally a conservative area, as a sign of her strength.

Republicans point to a Tipirneni ad showing her in medical scrubs wearing an Apple Watch and note that she hasn't worked as a physician since that device was invented. It was a way to insinuate she quit medicine over a malpractice lawsuit, something she denies.

RELATED: Tipirneni outraises Lesko as Arizona's CD8 race enters final stage

The battles underscore an intensity usually lacking in this part of Arizona and are another sign that Republicans have anxiety about the coming congressional midterm elections, when the president's party historically loses seats on Capitol Hill. The volatility and chaos of President Donald Trump's first term has contributed to a sense of dread among many in the GOP.

"There are obvious reasons for Republicans to be concerned. The president's approval rating isn't great, (and) special election numbers on the whole are not great for the GOP," said Geoffrey Skelley, a political analyst at the University of Virginia's Center for Politics.

Polling on the generic preference for Democrats or Republicans in Congress has improved for the GOP, potentially stabilizing fundraising and helping calm jittery nerves of vulnerable incumbents, Skelley said. All that will get a fresh appraisal after Tuesday.

"In that sense, I can see the outcome (in Arizona) mattering," Skelley said.

Why it matters

The election offers Democrats a long-shot possibility of narrowing GOP control of the House.

But a Lesko win by small numbers, say, less than 10 percentage points, is sure to be an ominous sign about Republican prospects in the fall elections. Right now, Democrats need to win 23 seats to retake the chamber.

"All of these special elections are being nationalized," said John McGlennon, a government and public-policy professor at the College of William and Mary in Virginia. "We see very high levels of voter engagement compared to other midterm election years, and the current nature of our political system, with the high polarization between the political parties, makes everything seem more national in scope."

MORE: Lesko, Tipirneni contrast views on health, taxes and guns

There have been eight federal special elections across the country since the 2016 elections. Democrats can point to improvement in all of them.

The party posted narrow, stunning victories in an Alabama Senate race and a Pennsylvania House race. Trump won Alabama statewide by 28 percentage points, and he won the Pennsylvania district by nearly 20 percentage points.

Five other races went to Republicans but by smaller margins than the party has seen in recent elections.

Mike Estes, for example, won a special election in Kansas last year by 7 percentage points. His predecessor, Mike Pompeo, who quit the House to join the Trump administration, won that seat by 32 points in 2016.

Similar outcomes played out in South Carolina, Montana and Georgia. In Utah, a third-party candidate also splintered GOP votes in a race there.

MORE: Lesko, Tipirneni clash over border-wall funding

In California, Democrats overwhelmingly won a race they easily won in 2016 as well, suggesting the common thread was not rejecting the party of recent incumbents.

Arizona's Republican-heavy 8th District offers another chance — six months from the midterms — to see if Democrats can compete everywhere.

Who did The Republic endorse?

Another sign of the intensity in Arizona revolves around The Arizona Republic.

Both sides have pointed to the newspaper's endorsement of their campaign during the primary election. But those endorsements of Lesko and Tipirneni were made in races against other candidates, not each other, and The Republic's editorial board hasn't made an endorsement for the general election.

Both sides have made it less than clear that The Republic's editorial board did not endorse either of them for the general election. And both sides have accused the other side of misleading voters over the endorsement issue.

Lesko cites The Republic's primary endorsement of her at the top of her list of backers on her website.

An early mailer from the Republican National Committee similarly noted that Lesko is endorsed by The Republic, not clarifying that she was endorsed only for the February primary election.

For her part, Tipirneni ran a TV ad that prominently notes, "The Arizona Republic endorsed her, saying Tipirneni could cut through the vitriol in Congress."

The ad did note that the endorsement appeared Feb. 5, though voters could be forgiven if they didn't know that was for the Democratic primary.

If Tipirneni trumpeted The Republic's view that represented a possible change in Washington, Lesko could point to a similar highlight published the same day.

"What really sets Lesko apart from this right-wing field of candidates is that she enjoys the advantage of actually making things happen — big things," The Republic's endorsement said.

Ballots show heavy GOP presence

Apart from the polls, early voting in the race underscores how it is largely being decided by Republicans.

Nearly half the ballots received through Wednesday came from registered Republican voters, according to figures tracked by the Secretary of State's Office. By comparison, 28 percent came from registered Democrats. The rest came from independents and members of other parties.

Republicans also have had a small turnout advantage over Democrats in the race.

The numbers don't reflect who the voters selected, but suggest many of them consider themselves Republicans.

If everyone voted in line with their party affiliation, Tipirneni would need to win nearly 90 percent of independents to match Lesko's GOP support.

RELATED: Attack ad on Debbie Lesko decried as 'lies'

Democrats are not suggesting they are winning nearly every independent vote, but they do think there's an underappreciated demographic in the race: Republicans crossing over to vote for the Democrat.

If Tipirneni attracted 20 percent of Republicans and won independents by just 10 percentage points, she could lose 10 percent of her party's voters and still be within 5 percentage points of Lesko.

How the party loyalists and independents come down will determine whether the race ends as an underwhelming Republican performance or a Democratic shocker that would reshape Congress even before November's elections.

A tough place for Democrats

The Arizona election comes a month after Democrat Conor Lamb's upset win over Rick Saccone in a usually conservative district in western Pennsylvania.

That district has some superficial similarities to Arizona's 8th District, which has some wondering if Democrats can do it again.

For one, Trump won both districts by 20 or more percentage points. And both special elections became necessary after eight-term Republican incumbents were toppled by sexual-misconduct scandals.

RELATED: Nation focused on AZ election to replace Franks

But there are key differences that set the races apart.

Before this year, Republicans were winning in Pennsylvania, but Democrats maintained a voter-registration edge. That suggests that people there were at least open to voting for a Democrat in a way that hasn't happened yet in the Arizona district, where most people register and vote Republican.

That race also featured a third-party choice who collected more votes than the final margin separating Lamb and Saccone. There is no third-party choice on the ballot in Arizona.

Also, Lamb sold himself as a former prosecutor who supported gun rights and personally opposes abortion rights.

RELATED: 5 takeaways from the 8th District congressional primaries

Tipirneni is a doctor who calls for a public option to achieve universal health-care coverage. She favors limited gun-safety reforms and welcomed a student from the Parkland, Florida, high-school massacre to help in the campaign's final weekend.

Republicans keep spending

If those positions put Tipirneni at odds with conservative voters, national Republicans aren't acting like the race is in the bag.

The Republican National Committee has spent $527,000 trying to help Lesko. The National Republican Congressional Committee has chipped in $383,000. The Congressional Leadership Fund, linked to House Speaker Paul Ryan of Wisconsin, has poured $102,000 into the race.

Democrats have notably stayed out of the race, but outside groups supportive of the party have waded in.

The Progressive Turnout Project, for example, has spent $33,000 largely on ground operations. People for the American Way put $17,000 in the race. The AAPI Victory Fund, a group that supports Asian American and Pacific Islander voters, has spent $5,000 to help Tipirneni, who is an immigrant from India.

RELATED: Tipirneni gets backing of group opposed to corporate campaign cash

Campaign-finance reports from earlier this month show that Tipirneni outraised Lesko overall and from those living in the district who gave at least $200.

At the time the reports ended, on April 4, Tipirneni had $125,000 in cash; Lesko had $54,000.

Lesko has reported raising at least another $82,000 since then, mostly from PACs. Tipirneni has reported at least another $50,000, mostly from individuals.

In the final days of the race, Lesko was scheduled to go to Washington for a fundraiser with Ryan, and House Majority Leader Kevin McCarthy, R-California, was scheduled to come to Arizona to help her raise money.

End Citizens United, a Washington-based political-action committee that helped Democrats raise money in their recent upset wins in Alabama and Pennsylvania, claims to have steered $100,000 to Tipirneni's campaign.

Ady Barkan, a progressive health-care activist whose videotaped pleadings with U.S. Sen. Jeff Flake, R-Arizona, last year briefly became a viral hit, has formed a group trying to raise money for Democrats, starting with Tipirneni.

RELATED: Democratic activist launches six-figure ad blitz in CD8 race

After Tuesday, both parties will shift their attention to the next race, a special election in Ohio in August, and the November midterms across the country.

Jason Kimbrough, a spokesman for the Tipirneni campaign, offered an early postmortem for the Arizona race that both sides might accept.

"Regardless of the outcome on Tuesday," he said, "the ultimate takeaway for both parties may be to really listen to the voters in that district and not just take a cookie-cutter approach, ripping pages out of the playbook, presuming the party lines will work like they used to."