Jeff Flake, who is retiring after his fierce criticism of Trump made his political future in the state untenable.
The open Senate race is among the nation's most competitive, and is consequential for a state that is on the cusp of electing its first woman senator.
Other contenders for McCain's seat include Kirk Adams, 45, the governor's chief of staff and a one-time candidate for Congress; Arizona state Treasurer Eileen Klein who oversaw the state's university system; and former U.S. Representative John Shadegg, 68, who served 16 years as a member of Congress from northern Phoenix.
All three Republicans had distanced themselves from McCain, who frequently feuded with Trump, and Ward suggested that his family's announcement on Friday that he was stopping medical treatment was timed to hurt her campaign. Kelli Ward of Lake Havasu City and former Maricopa County Sheriff Joe Arpaio of Fountain Hills, according to unofficial results from the Secretary of State.
While McSally has talked up her relationship with Trump on the stump, Arpaio and Ward have slammed her on it, claiming she's a duplicitous flip-flopper in the mold of Flake and Sen.
McSally will now face U.S. Rep. Kyrsten Sinema in November.
Representative Martha McSally speaks during her primary night gathering on August 28, 2018 in Tempe, Arizona. But 2018 would be a disastrous year for the GOP to end the streak, with partisan control of the Senate likely to hang in the balance. "This is how I see this campaign", McSally said. But Trump's surprise endorsement of DeSantis in December appears to give the congressman an edge heading into Tuesday's contest.
If those margins hold up when the precincts fully report, it looks like Arizona will remain a red state in November - perhaps especially with McSally leading the ballot. The CNN survey found that 67 percent of Democrats had a favorable opinion of McCain, while just 33 percent of Republicans had a favorable view of the GOP senator.
It also represents a change in direction for Florida Democrats, who have been out of the governor's office in the state for 20 years; two more moderate candidates fell short against Rick Scott in 2010 and 2014. The governor was expected to easily win his party's nomination for a second term in Tuesday's gubernatorial primary.
But the races, especially in Arizona, will take on special meaning following the death of Sen. Democrats are feeling bullish because, while Flake saw his party moving too far in Trump's direction for him to win the GOP primary, the president won Arizona overall by less than 4 points in 2016.
Only five states remain to pick candidates in early September before full attention turns to the November election, when all 435 House seats and 35 of the 100 Senate seats will be at stake.
Polls have shown a close race. They recruited former U.S. Rep. Gwen Graham, the daughter of a popular former governor and U.S. senator, who had won support from business in the past. Stitt is using his personal fortune to attack Cornett for not being sufficiently loyal to Trump and his administration.
Democrats have already nominated Drew Edmondson, former state attorney general. She'll face off with the victor of a seven-way Democratic primary in November.