AUSTIN, Texas — In the growing Democratic presidential field, they seem like a study in opposites.

One’s 77, a democratic socialist from the U.S.-Canada border state of Vermont, who exudes a curmudgeonly grumpiness and bursts with detailed policy proposals. The other’s a boyish 46-year-old native of the U.S.-Mexico border city of El Paso, Texas, who livestreams his skateboarding prowess and offers hopeful but vague paeans to tolerance and cooperation.

Bernie Sanders and Beto O’Rourke may represent different poles among the dozen-plus Democrats vying for the White House, but they have key commonalities that now inject special tension into their rivalry as they ramp up their campaigns.

Both lead the pack in fundraising and have built substantial campaign treasuries on thousands of small donors nationwide rather than using the more traditional model of a small core of major financial backers.

They also strike chords with the same part of the electorate. In their last races, each rose on a strong appeal to young voters.

Now, though, it’s not clear both can exploit their strengths while going head-to-head.