O'Rourke launch is a final puzzle piece in Dem primary race

Beto O’Rourke wrote: "I'm really proud of what El Paso did and what El Paso represents. It's a big part of why I'm running." (Source: Beto O'Rourke/Facebook/MGN)

WASHINGTON (AP) -- The contours of the Democratic presidential primary came into clearer focus this week with Texan Beto O'Rourke's entry into the race.

O'Rourke's candidacy is one of the final puzzle pieces in a contest that will be shaped by questions about race and gender, political ideology and generational change. Vice President Joe Biden is now the only major contender still on the sidelines.

The field has been awaiting O'Rourke's decision for months. He narrowly lost the Senate race in conservative Texas in November, but became a political celebrity in the process, demonstrating an easy connection with voters and an eye-popping ability to raise money from small donors.