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FLAGSTAFF, Ariz. — Senator Bernie Sanders of Vermont took on one of Arizona’s most contentious political figures at a rally on Thursday, calling Sheriff Joe Arpaio of Maricopa County a bully and accusing him of “un-American” behavior.

Mr. Sanders, speaking to a crowd of about 2,800 people at Twin Arrows Navajo Casino Resort here, also pledged to devote more federal resources to Native Americans, who he said “face appalling levels of inequality.”

The rally came days after Mr. Sanders’s wife, Jane Sanders, had an impromptu discussion with Sheriff Arpaio at his so-called Tent City in Maricopa County, where jail inmates are housed under the hot sun. Sheriff Arpaio has said that the conditions there are no worse than those faced by many United States soldiers overseas.

Mr. Sanders said that Sheriff Arpaio, who is well known for his hard-line stance on illegal immigration, had “ambushed” his wife. “She asked him about racial profiling, and he didn’t have an answer,” Mr. Sanders said. “She asked him about conditions in Tent City and other abuses that he has perpetuated, and he didn’t have an answer. You know what, he cannot have an answer, because what he is doing is un-American and uncivilized.”

He told the cheering crowd, “If elected president, we are going to pass comprehensive immigration reform and a path toward citizenship, whether Mr. Arpaio likes it or not.”

Mr. Sanders also repeated his vow to remain in the presidential race, saying he believes he has a path to winning the Democratic nomination over Hillary Clinton. Arizona’s primary elections will be held on Tuesday.

Mr. Sanders was introduced at the rally on Thursday by Katherine Figueroa Bueno, a teenage immigration activist who, at the age of 9, saw her parents being detained on television in a workplace raid led by Sheriff Arpaio.

“Arpaio took away my childhood, because I had to grow up from one week to another,” she said. “I am one of millions of other kids that are left behind.”

“I want all deportations to stop, that’s why we need Bernie Sanders to be our president,” he said.

Mr. Sanders vowed to prevent others from experiencing what Ms. Figueroa Bueno did. “It’s easy for bullies like Sheriff Arpaio to pick on people who have no power, but if I’m elected president, the president of the United States does have the power,” he said. “Watch out, Joe!”

Mr. Sanders also called for an end to “systemic injustice” faced by Native Americans, a quarter of whom he said live in poverty. He said that young Native Americans faced low graduation rates and high suicide rates, and that one Native American woman in three would be raped during her lifetime.

“The Native American people have been lied to, they have been cheated and negotiated treaties have been broken,” he said. “We owe the Native American people so, so much.”

The senator also weighed in on another contentious topic. “The city of Washington has a very good football team, but it doesn’t have to be called the Redskins,” he said.