US Democratic presidential candidate Bernie Sanders has taken a tour of the state of Arizona as he tries to overtake rival Hillary Clinton ahead of the state's Democratic presidential primary.

On Saturday morning, Sanders also visited the US-Mexican border, receiving cheers from people on the other side of the boundary who identified themselves as deported US military veterans.

The independent senator from Vermont promised to expand programs created by US President Barack Obama that protect undocumented immigrants from deportation and allow them to work legally in the US.

Sanders called the controversy over immigration "trumped up," referring to insulting remarks by Republican frontrunner Donald Trump about Mexican immigrants and proposing the construction of a wall on the US-Mexican border.

Later Saturday night, Sanders drew a boisterous crowd of about 3,300 to the state fair grounds in Phoenix, according to campaign estimates.

"Bernie Sanders — rah rah rah — we don’t need no Super PAC," the crowd chanted before he took the stage, riffing on one of Sanders' main talking points.

Sanders boasts of the roughly 2 million small donors funding his political campaign, comparing it with Clinton's many wealthy donors and her well-funded political action committee (PAC).

Sanders' consistency on progressive issues over several decades has attracted many voters, including 23-year-old Phoenix resident Brenden Parks.

The Honeywell warehouse employee said he sees a brighter future for his 3-year-old son under a Sanders presidency given the candidate's promises of single-payer health care and free college.

"I understand there's going to be a tax increase on the middle class," Parks said, "but the benefits will outweigh it."

Michael Mora, 30, of Phoenix said he trusts Clinton "zero percent," forming a zero with his hand. Clinton has changed positions too many times over the years, he said.

Economic issues are the deciding factor for him. "People are saying (Sanders) is trying to give away free stuff. That's not what he's trying to do," Mora said. "He's trying to make everything as fair for everybody as possible."

Sanders, 74, is a leading proponent of issues such as income inequality, universal healthcare, parental leave, climate change, and campaign finance reform.

He has also long been critical of US foreign policy and was an early opponent of the wars in Iraq and Afghanistan.