Former Texas congressman Beto O'Rourke, whose ultimately unsuccessful bid for the U.S. Senate in 2018 earned him a fervent and national following, announced Thursday that he is running for president in 2020.

"This is a defining moment of truth for this country and for every single one of us," O'Rourke said sitting alongside his wife, Amy, in his official announcement video released Thursday morning. "The challenges that we face right now; the interconnected crises in our economy, our democracy and our climate have never been greater."

In kicking off his campaign, O'Rourke hit on a laundry list of policy issues that will dominate the discussion throughout the Democratic primary, from health care, to combating climate change to reframing the debate around an issue President Donald Trump has sought to define throughout his first two years in office: immigration.

"All of us, wherever you live, can acknowledge that if immigration is a problem, it's the best possible problem for this country to have, and we should ensure that there are lawful paths to work, to be with family, and to flee persecution," O'Rourke said.

O'Rourke also said his campaign will be about confronting "the hard truths of slavery, and segregation and suppression in these United States of America."

The native Texan also previewed an upcoming event in his hometown of El Paso on March 30, which will likely serve as the official launch of his presidential bid.

O'Rourke, 46, opened his presidential campaign in the crucial early voting state of Iowa -- his first visit -- embarking on a three-day swing through the state Thursday afternoon to introduce himself to voters and begin to distinguish himself from a crowded Democratic field of more than a dozen candidates.

At his first stop in a coffee shop in Keokuk, he took questions from the crowd on a range of issues, including healthcare, marijuana, the Green New Deal, and the Democratic field brimming with contenders.

O'Rourke made his pitch for "guaranteed, high-quality health care" -– underscoring the "guaranteed" portion to emphasize his support for ensuring Americans are not only covered by health insurance but also can access the benefits of health insurance without steep costs.

He also noted that while universal health care brings a hefty price tag, he said he believes the costs outweigh those of losing a loved one or productivity from those who are sick.

O'Rourke also appeared unfazed by the challenge of joining an already crowded field, instead promising Iowans he would run a positive campaign.

"We hold each other accountable not just for what we promise and enact or fail to enact but how we conduct ourselves on the campaign trail," O'Rourke said. "Critically important that we not denigrate, demean any other candidate. We don't talk about their personal lives."

He also pushed for all the candidates to back the eventual Democratic nominee, since he said, any candidate running as a Democrat "would be far better than the current occupant of the White House."

O'Rourke closed out his first stop by declaring to the applauding crowd: "I'm running to serve you as president of the United States of America."

Back in Washington, President Donald Trump, when asked about his latest 2020 competitor, responded that he watched TV coverage of O'Rourke's Iowa appearance, and commented with mock amazement, "He has a lot of hand movement ... is he crazy or is that just the way he acts?"

"I have actually never seen anything quite like it. Study it, I'm sure you'll agree," Trump said to reporters at an Oval Office photo-op.

O'Rourke continued his first official day as a presidential candidate with a string of intimate, town-hall-style events, taking questions from voters and outlining why he believes he is qualified to be President of the United States.

At an earlier campaign stop, O'Rourke hearkened back to his days campaigning for the Senate last year and told the crowd he hopes to run his presidential campaign in a similar way.

"When I ran for Senate in Texas ... I visited all 254 counties in the state...it took 70 years for someone to come back and show the common decency and respect of being there ... that's how I think we distinguish ourselves, not just from another candidate but from how politics is done in this country today," O'Rourke said in Fort Madison.

ABC News' Paula Faris asked O'Rourke after his third campaign event in Burlington Thursday about what sets him apart from the crowded Democratic primary field.

"I'm going to allow people to determine what sets us apart from one another," he said. "All I can tell you is that I want to be able to bring people together. We have a history of being able to do that in El Paso and ensuring our party affiliation geography race doesn’t separate us or keep us away from this moment."

"I think you have to believe in the genius of this country and the only way to do that is to bring everyone in, take everyone in and write no one off. So I'm for everyone, whether or not that's a winning strategy it's the only way I know how to run," O'Rourke said when asked by ABC News if he has to be a "street fighter" to beat Trump.

O'Rourke also addressed criminal justice reform at the Burlington stop, posing to the crowd in Beancounter coffee shop, "Why is it that a Texas woman who violated election law goes to prison for a similar amount of time to Paul Manafort?"

While in Iowa, O'Rourke plans to visit eight counties that voted for Barack Obama in 2012 before flipping to Trump in 2016, a sign that he is already hoping to target voters that have gravitated away from the Democratic Party in recent years.

O'Rourke will also campaign this Saturday for Democratic state Senate candidate Eric Giddens, an appearance confirmed earlier this week in a video posted on Twitter.

However, the trip to Iowa this weekend comes as O'Rourke appears to have lost early ground against his potential Democratic rivals.

While a December 2018 Des Moines Register poll of likely Iowa Democratic caucus-goers showed O'Roruke garnering 11 percent of the vote, a poll by the same outlet released this past weekend showed his support had dipped to just 5 percent.

But despite the likely difficult road ahead, O'Rourke's foray into the presidential race is the culmination of an unlikely political rise that began with the three-term congressman and former El Paso City Councilman's decision to challenge Republican Sen. Ted Cruz in the 2018 U.S. Senate race in Texas.

Following his narrow loss to Cruz, the months of speculation around O'Rourke's political future kept him in the conversation about possible contenders for the Democratic Party's presidential nomination, despite questions over whether or not a failed Senate candidate with a thin congressional record could be a viable candidate.

However O'Rourke's unorthodox Senate campaign, which shunned traditional strategists and instead relied on the candidate's organic appeal, broke fundraising records and earned him a national profile that he now hopes will take him all the way to the White House.

His off-the-cuff style, typified by his campaign's frequent livestreams that showed the candidate in intimate settings with supporters and his family, endeared him to a national audience, even if it did not ultimately earn him a seat in the U.S. Senate.

In an interview published Wednesday in Vanity Fair magazine, O'Rourke stopped just short of announcing a presidential bid but made it clear he believes he can find success in the Democratic field.

"You can probably tell that I want to run,” O'Rourke said. "I do. I think I’d be good at it. This is the fight of our lives. Not the fight-of-my-political-life kind of crap. But, like, this is the fight of our lives as Americans, and as humans, I’d argue."

Last month O'Rourke teased an upcoming announcement that led many to believe he would seek the Democratic nomination for president, saying that he and wife Amy had made a decision regarding his political future.

"Amy and I have made a decision about how we can best serve our country," O'Rourke told The Dallas Morning News in a statement confirmed by ABC News. "We are excited to share it with everyone soon."

That statement followed a high-profile interview with Oprah Winfrey in early February, where O'Rourke said we would make a decision on a presidential run by the end of the month.

"We want to play as great a role as possible making sure that this country lives up to our expectations, to the promise, to the potential that we all know her to have," O'Rourke said.

A few weeks after that interview O'Rourke led a counter-rally during President Donald Trump's visit to El Paso, an enticing split-screen that provided him with a platform to directly take on Trump in his hometown.

The former congressman has also visited the state of Wisconsin earlier this month, meeting with students at a technical college in Milwaukee and at the University of Wisconsin in Madison.

But as he enters a crowded Democratic primary field that already includes six U.S. senators, O'Rourke will likely face questions about whether he has the experience to be commander-in-chief.

The political path of the former El Paso city councilman who went on to represent the city for three terms in the U.S. House has garnered comparisons to President Abraham Lincoln, who ran unsuccessfully for the U.S. Senate in 1858, only to win the presidency two years later.