When President Trump finds himself under attack or slipping in popularity, he often holds a rally in a place like this: a diverse blue city that’s home to liberal protesters but surrounded by red suburbs and rural towns filled with Trump supporters who will turn out in droves.

It happened in the first weeks of his presidential campaign, when he was dismissed as a sideshow and criticized for his comments on undocumented immigrants — only to be greeted by thousands of fans, along with protesters, at a rally at the Phoenix Convention Center. Then in March 2016, when Trump grew frustrated that he still hadn’t become the presumptive Republican nominee, he planned a massive rally in inner-city Chicago that attracted thousands of supporters but was canceled at the last minute because of the high number of protesters. This March, when his presidency seemed constantly under attack, Trump held a rally in Nashville that attracted at least 2,500 protesters.

Unlike rallies in states that are solidly Republican, these events allow Trump to highlight the deep division in the country — and force voters to pick a side.

In Phoenix, campaign organizers expected more than 10,000 supporters to show up at the convention center on Tuesday night, and numerous counterprotests were planned for outside the rally, which was organized by Trump’s campaign organization and not the White House. Local activists say they hope to outnumber the rallygoers, sending a clear message to the president after the Charlottesville rally this month that attracted neo-Nazis and white supremacists.

“By coming here in a time of national crisis and a national question of where people stand, he is doubling down on his bigotry, continuing to race-bait and speak to his base,” said Carlos García, executive director of Puente Arizona, which advocates for migrants.

President Trump waves as he walks across the South Lawn to board Marine One at the White House on Tuesday. (Andrew Harnik/AP)

Phoenix is home to some of the most organized progressive activists in the country, and they have provided a much-studied example of how to fight at a grass-roots level to challenge lawmakers and change policies that target undocumented immigrants. The Phoenix area gave liberals one of their few victories on election night last November: The ouster of longtime Maricopa County sheriff Joe Arpaio, who was accused of encouraging his deputies to employ racial profiling and enforce federal immigration laws in the Phoenix suburbs.

In July, Arpaio was convicted of criminal contempt in Arizona for ignoring a judge’s order to stop detaining people because he merely suspected them of being undocumented immigrants. His sentencing is scheduled for Oct. 5, and he faces up to six months in prison.

Last week, Trump told Fox News he is “seriously considering” issuing a pardon, possibly within a few days, because Arpaio was a “great American patriot” who had “done a lot in the fight against illegal immigration.” Arpaio told CNN that he has not been invited to attend the Tuesday night rally.

A pardon would be likely to ignite the anger of hundreds of activists who spent more than a decade peacefully pushing for change through traditional channels, along with the voters who chose to vote Arpaio out of office.

“A pardon for Joe Arpaio is a pardon for white supremacy,” Jess O’Connell, chief executive of the Democratic National Committee, said at a news conference here Monday.

White House press secretary Sarah Huckabee Sanders on Tuesday told reporters traveling with the president that Trump does not plan to announce a pardon for Arpaio at the rally.

“There will be no discussion of that today at any point, and no action will be taken on that front at any point today,” she said.

President Trump arrived in Arizona on Aug. 22, for a tour of the U.S.-Mexico border and a campaign-style rally. (The Washington Post)

Phoenix Mayor Greg Stanton (D) and other Democratic leaders in Arizona have urged Trump to not rally in their city this week, saying that it is too tense of a time and that he’s setting the stage for yet another violent clash. Police and local authorities are planning for tens of thousands of rallygoers and protesters to descend on downtown Phoenix. Early Tuesday morning, they closed streets near the convention center and installed barricades along the sidewalks aimed at keeping protesters separated from rallygoers. Many businesses and government buildings downtown plan to close early. Meanwhile, it’s August in the desert, and the temperature in Phoenix could reach 106 degrees on Tuesday afternoon.

There are worries that people might bring weapons to the rally — although they will not be allowed through security — or that armed citizen militias could show up, as they did in Charlottesville.

Protest organizers said one challenge will be managing the hundreds of people not affiliated with their groups who show up and want to make a statement. There is also the issue of simply keeping everyone hydrated. Organizers and local lawmakers are urging a peaceful demonstration.

It remains to be seen how Trump campaign officials will respond if rallygoers show up with Confederate flags or Nazi paraphernalia. Since the event is being paid for by the campaign and is not a White House event, organizers can kick out anyone they want and determine what signs, flags or clothing can be displayed. During the presidential campaign, unaffiliated vendors would often sell Confederate flags outside Trump’s rallies, and a few supporters would wear hats, shirts or patches featuring the flag. At an August 2016 rally in Kissimmee, Fla., a 27-year-old Trump supporter draped a Confederate flag, with “Trump 2016” printed on it, over a railing near the stage. It was quickly taken down by a campaign staff member and the local police.

While Democrats and immigration rights activists have been holding news conferences and speaking out against the president this week, Republicans have been quiet. No one answered the phone at the Arizona GOP offices on Monday or Tuesday.

Arizona’s two Republican senators, John McCain and Jeff Flake, have been critics of the president. Trump has tweeted praise of Kelli Ward, a former state lawmaker with far-right views and a long-shot Senate candidate who is challenging Flake.

Trump left Washington around lunchtime Tuesday. He was to first meet with Marines at a Yuma, Ariz., Border Patrol station, inspect a Predator drone and promote his administration’s push to tighten immigration enforcement. The rally was set to begin at 7 p.m. local time, 10 p.m. Eastern.

This will be Trump’s ninth rally in the state — and his fourth at the Phoenix Convention Center.

His first event at the convention center was on July 11, 2015, a few weeks after he announced he was running for president and gave a rambling speech that cast undocumented immigrants as criminals and “rapists.” Although those remarks prompted criticism and led several corporations to cut their business ties with him, the support for his campaign was evident in Phoenix, where he had to upgrade to a larger venue and then still had to turn away many supporters — a turnout that shocked many Arizonans. At the time, McCain accused Trump of having “fired up the crazies.” Protesters who attended the rally and were violently confronted by Trump supporters said they were stunned by this new level of animosity, which has now become the standard.

During a March 19, 2016, rally in the Phoenix suburb of Fountain Hills, where Arpaio lives, dozens of protesters used pickup trucks and their bodies to block the highway leading to the rally site to delay Trump’s motorcade. They carried signs that said “Stand Against Racism” and “Combat White Supremacy.”

At an Oct. 29 rally at the Phoenix Convention Center, a Trump supporter confronted reporters at the rally with shouts of “Jew-S-A!” and flashed a three-fingered hand gesture that resembled hate symbols flagged by the Anti-Defamation League.