President Trump focused on immigration Friday in Mesa, Ariz., in his second rally in three consecutive days. Mr. Trump was campaigning for Rep. Martha McSally, who is locked in a challenging race with Democratic Rep. Kyrsten Sinema to fill retiring Sen. Jeff Flake's Senate seat.

Mr. Trump spent much of the rally talking about undocumented immigrants, resurrecting the phrase "bad hombres" to describe criminals entering the country illegally. He said hospitals and schools were "overrun" with immigrants.

"The casualties in the Democrats' open border crusades are American families," Mr. Trump said, incorrectly saying that the Democratic Party supports drugs and criminals pouring into the country. He said that a Democratic victory in November would be a "bright flashing sign" to allow drug dealers and criminals to come into the country.

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Arizonans have also faced a barrage of negative ads by both candidates throughout the election cycle. Sinema has also raised nearly $4 million more than McSally. Although Mr. Trump won Arizona in 2016 by nearly four points, Democrats are hopeful that they can capture Flake's seat, if younger, urban and Hispanic voters turn out in November. The CBS News Battleground Tracker rates the race as "Edge Democrat."

Mr. Trump continued his attacks on Democrats, whom he called an "unhinged mob."

"Vote for the jobs, not for the mobs," he said, adding that the Republican majority was "very fragile." He urged rally goers not to be "complacent." He also targeted some Democrats by name, including Sen. Elizabeth Warren, who recently released a DNA test proving that she has a Native American ancestor in response to attacks from Mr. Trump.

"We can no longer call her Pocahontas! I don't know what I'm going to do," Mr. Trump said of Warren, claiming the test showed that she had no "Indian blood."

The race in Arizona has become increasingly contentious, with McSally accusing Sinema of "treason" at a debate earlier this week. Sinema has drawn fire for comments made during a radio interview in 2003, when she told the radio host to "go ahead" if he wanted to hypothetically join the Taliban.

Mr. Trump also criticized Sinema for those comments. He brought McSally to the stage at one point, where she continued her attacks on Sinema. She promised to fulfill Trump campaign promises, notably building a border wall between the U.S. and Mexico.

"Martha's opponent is a far-left extremist," Mr. Trump said about Sinema, adding that she was being "protected by the fake news media."

"A vote for Kysten Sinema is a wasted vote, but more importantly it's a dangerous vote," Mr. Trump said, adding that voting for McSally would be the "second greatest vote you ever cast." "The first greatest vote was for me," he said.

Mr. Trump visited Montana Thursday evening to rally for Republican Senate candidate Matt Rosendale. Mr. Trump focused heavily on illegal immigration in his speech, and will likely do so at Friday's rally as well, given Arizona's proximity to the U.S.-Mexico border.

"This will be an election of Kavanaugh, the caravan, law and order and common sense," Mr. Trump said, referring to a caravan of migrants from Honduras on their way to the American border. "As you know, I'm willing to send the military to protect our southern border if necessary." He also said at one point that "Democrats produce mobs, Republicans produce jobs."