GREELEY — Donald Trump continued to question Colorado’s first mail-ballot presidential election in his second visit in as many days to the crucial swing state.

“Do you think those ballots are properly counted?” he asked the crowd Sunday at the University of Northern Colorado.

“I know they are saying, ‘Oh, of course, it’s all legitimate,’” he added. “Perhaps I’m a more skeptical person.”

The Republican nominee’s opening remark about voter fraud in Colorado echoed his comments Saturday at a Jefferson County rally. But Colorado election officials are pushing back against the suggestion of a rigged system.

Republican Secretary of State Wayne Williams — a critic of the 2013 measure that implemented the current system — suggests “vote fraud is rare.”

Reacting to Trump, Denver elections chief Amber McReynolds said Sunday the current mail-ballot process includes more checks than prior presidential elections.

“From my perspective, it’s just a lack of understanding of all the safeguards and all the processes that we have in Colorado,” she said.

Trump’s visit came as a Republicans look to close a deficit in the early voting. Democrats held a 27,000-ballot advantage through Friday morning, the latest numbers available.

A new CBS/YouGov poll showed the presidential race is narrowing, as Trump is essentially tied in Colorado with Hillary Clinton — a shift from the Democrat’s comfortable lead in recent weeks.

Clinton received 42 percent and Trump registered 39 percent in the head-to-head poll of likely Colorado voters conducted last week. The close nature of the race is not unexpected, as President Barack Obama won Colorado by roughly 5 percentage points in 2012.

At numerous points in his 45-minute speech, Trump urged his supporters in the campus arena — numbering at more than 3,000, according to local officials — to “get those ballots in.”

The early numbers showing Democrats with the advantage may not foretell the final result Nov. 8, as evidenced by Trump fans at the event.

Thomas Crawford, a registered Democrat from Denver, traveled to Greeley for the rally. He and wife Martha, a longtime Democratic voter, cast ballots for Trump.

“I think the Clintons have sold this country down the river,” said Crawford, a 49-year-old salesman.

“Trump’s not a politician,” added Martha Crawford, 63. “He’s going to drain the swamp.”

The FBI investigation involving former U.S. Rep. Anthony Weiner and e-mails discovered on his laptop that possibly link to Clinton only invigorated Trump’s supporters in the crowd. As Trump made his speech, the FBI reported that it obtained a search warrant for e-mails tied to Clinton.

Trump called the revelation about the new investigation a “bombshell.”

“Hillary Clinton is not the victim, by the way. You, the American people, are the victims of the corrupt system,” Trump said.

In Colorado’s energy hub, Trump made clear he supports hydraulic fracturing, known as fracking, and criticized his Democratic opponent for requiring so many restraints that it makes it near impossible.

Trump said fracking has an “unbelievable impact” on the nation’s energy production — a sentiment he heard in a recent meeting with oil and gas executives in Denver. “We have under our feet,” he said, “so much wealth.”

To do it properly, Trump outlined only three requirements. “I want crystal clear, crystal clean water. I want such clean air. And I want safety,” he said. “Other than that, that’s what I want.”