PHOENIX – If Ruben Gallego is going to give Democrats their fourth straight U.S. Senate victory in Arizona, he’s probably going to need support from an unlikely group: Donald Trump voters.

Gallego and his GOP rival, former television news anchor Kari Lake, are both targeting undecided Republicans in a contest that will test the strength of Trump’s coattails. Ticket-splitting voters are increasingly rare in an era when partisan loyalty reigns, but they could be central in determining which party controls the Senate.

For Gallego, that means winning over voters like Winfield Morris, a 62-year-old Republican farmer and rancher who plans to vote for Trump for president but can’t get behind his loyal ally in the Senate race.

Gallego’s strategy relies on Democrats keeping their own supporters united, getting a majority of independents, and picking up a small but decisive share of Republicans by appealing to conservatives who dislike Trump.

Republicans have had a hard time replicating Trump’s coalition. Celebrity candidates who are close to Trump but lack strong ties to the GOP establishment have struggled to replicate his success.

Both Lake’s and Gallego’s messaging reflect the importance of undecided Republicans to the outcome of the race. Both are running ads focused on border security, almost exclusively so in Lake’s case.

In Arizona, Gallego is hoping to replicate the model that has propelled Democrats to narrow statewide victories since Trump’s first victory, including Sens. Kyrsten Sinema and Mark Kelly and Gov. Katie Hobbs, who defeated Lake in 2022.

He’s getting plenty of help. Democrats so far have outspent Republicans on advertising by a wide margin on the race, according to AdImpact, which tracks campaign ad spending.

In 2020, Republican Senate candidate Martha McSally privately fretted that she was running behind with Trump voters, which turned out to be the case. While Trump lost Arizona by 10,457 votes — .03 percentage points — McSally lost by 78,806 to Kelly, indicating tens of thousands of voters split their tickets.

Some observers say Gallego fits the profile of the kind of candidate who could replicate the path forged by Kelly, a tough-talking former astronaut.

Ruben is a legitimate tough guy,” said Stacy Pearson, a Phoenix-based Democratic strategist, who ran the successful 2016 campaign to oust Maricopa County Sheriff Joe Arpaio.

Associated Press writers Jack Dura in Bismarck, North Dakota, and Amy Beth Hanson in Helena, Montana, contributed to this report.