With just one day until voters cast their midterm ballots, Arizona's Senate battle remains one of the tightest races on the map -- with Republican nominee Martha McSally and Democratic rival Kyrsten Sinema trading the lead in the final burst of polling.

McSally held onto a 1-point lead in an ABC 15 poll, but an Emerson College survey gave a 1-point edge to Sinema. Both surveys put the race within the margin of error, underscoring how unpredictable the race has been for weeks. The Real Clear Politics average shows Sinema with just over a 1-point lead.

As with many states, though, a huge chunk of the electorate has already voted thanks to early or absentee voting. According to the Arizona Secretary of State’s office, nearly 80 percent of the ballots cast for the election will have been filled out before Tuesday’s election.

“The work we’re doing over these last five days is to communicate with voters who have not turned in their early ballot,” Sinema told reporters in Phoenix last week. “I’m just working hard to earn the vote and the support of Arizona.”

McSally spent the weekend hitting the stump. She is slated to campaign with Arizona Gov. Doug Ducey, who is running for a second term. A Fox News Poll released last week had Ducey with an 18-point lead over Democrat David Garcia, among likely voters.

McSally, the first female U.S. fighter pilot to ever see combat, has been offered support by the highest levels of the Republican Party, with an endorsement from President Trump, who held a “Make America Great Again” rally in Mesa, Ariz.

MCSALLY, SINEMA TARGET ARIZONA'S UNDECIDED VOTERS AS SENATE RACE ENTERS FINAL DAYS

“It’ll be one of the best votes you’ve ever had,” Trump said at the rally. “I need you to get your friends, get your family, get your neighbors, get your co-workers and get out and vote for Martha McSally.”

The president’s eldest son, Donald Trump Jr., also campaigned for McSally in Arizona.

“We need your help, we need you to get out there,” Trump Jr. said last week. “[The president] needs people like Martha fighting for him.”

Meanwhile, Sinema has opted out of campaigning with high-profile Democratic figures.

Sinema, whose record in the Arizona state Senate leaned left, has tried to position herself as a moderate since being elected to the U.S. House of Representatives in 2012. Sinema has even supported Trump on some issues, including backing his $1.3 billion spending bill earlier this year.

“The only poll that matters is when they count up the ballots on Election Night,” McSally told Fox News over the weekend. “I know the importance of making sure we get to every last voter out there who is maybe sitting on the sidelines, build enthusiasm and make sure we get across the finish line.”

Arizona is one of five key "toss-up" races, according to Fox News' Power Rankings. The others are Indiana, Florida, Missouri and Nevada. As of Monday, Power Rankings puts 50 Senate seats in the Republican column (including those likely or leaning Republican, and GOP seats not up for election this year), and 45 in the Democratic column.

On the House side, Democrats remain well-positioned to reclaim the majority after multiple cycles in the minority. The Real Clear Politics map shows 202 House seats tilting Democratic, and 194 tilting toward Republicans, with 39 in the “toss-up” column. Fox News’ Power Rankings similarly puts the split at 207 seats for Democrats and 199 for Republicans, and the rest up in the air. It takes 218 seats to claim a majority.

Fox News' Melissa Chrise and Alicia Acuna contributed to this report.