Democratic 2020 presidential candidate Beto O'Rourke speaks during a campaign stop at The Beancounter Coffeehouse & Drinkery in Burlington, Iowa, U.S. March 14, 2019.

A rare blend of personal magnetism and fund-raising might makes Beto O'Rourke immediately formidable in the crowded Democratic presidential race.

But O'Rourke faces circumstances and competition radically different from those that made him a political sensation. He can't skateboard past them as easily as in his 2018 U.S. Senate campaign.

His strengths sparkle in plain sight. After three unremarkable terms as a House member from El Paso, O'Rourke lit a fire among Democrats nationally in his bid to knock off incumbent Texas Republican Ted Cruz.

He did it by traveling indefatigably, meeting voters in red and blue precincts alike. Iowans reward that kind of campaigning in the caucuses that kick off the nominating process next February.

He did it by attracting massive crowds with youthful insouciance and a hopeful, unifying message amid bitter partisan divisions. Barack Obama emerged the same way in his 2004 Democratic convention speech declaring, "There's not a liberal America and a conservative America, there's the United States of America."

And he did it by speaking fluently on behalf of immigration and racial justice, powerful themes for the key Democratic constituencies of Latinos, African-Americans and white liberals. O'Rourke's impassioned defense of black athletes who kneeled during the national anthem made him a viral video phenom.

Deepened by Democratic antipathy toward Cruz, all that created a spectacular small-donor fund-raising machine. It raked in $79-million – more than Sen. Bernie Sanders of Vermont raised in 2015 as his primary challenge to Hillary Clinton took off.

That was then. Now O'Rourke confronts more challenging terrain for the Democratic nomination race.