Arizona voters cast their first ballots this week for the November general election, with the potential to decide which party controls the U.S. Senate.

On this weekend's "Sunday Square Off," we have the latest news on the Senate race: What the polls tell us about the contest between two Arizona congresswomen, Republican Martha McSally and Democrat Kyrsten Sinema.

The winner will be the first woman to represent Arizona in the U.S. Senate.

Early ballots will be mailed to voters starting Wednesday. The deadline to register to vote is Tuesday. Go to servicearizona.com to register.

Also on "Square Off":

-Gov. Doug Ducey leads Democrat David Garcia in the polls but he's crushing Garcia in the money race.

-Phoenix mayoral candidate Daniel Valenzuela finally concedes he can't hold down two full-time jobs if he's elected mayor.

-Arizona voters like the idea of banning a bunch of new taxes in Prop 126. So why are Democrats and Republicans coming to together to say it's a bad idea?

-How one group is finding new ways to register young voters.

Toss-up in AZ Senate race; governor up 50-1 in TV race

Polls show Arizona's U.S. Senate race is a toss-up. In the governor's race, Doug Ducey and his allies are outspending Democrat David Garcia by 50 to 1 on TV.

Arizona voters favor banning new taxes. Should they?

Prop 126 on the November ballot would make it illegal to tax all services in Arizona. Why do Democrats and usually anti-tax Republicans oppose it?

How ban on taxes might affect Arizona economy

Arizona is more dependent than most states on sales taxes to pay for government services. So why is it a good thing to declare a growing part of the economy off-limits for taxes?

How one group is registering young voters

NextGen Arizona says it's signed up 20,000 young voters for the 2018 midterms. But is the group funded by a Democratic billionaire registering all voters no matter their party?

"Sunday Square Off" airs at 8 a.m. Sundays on 12 News, after NBC's "Meet the Press" with Chuck Todd.