Judy Woodruff:

Most of the Democratic candidates for president are here in Des Moines, Iowa, tonight for a dinner to rally their party and fire up their voters.

No one has more on the line than former Vice President Joe Biden, who is making his third run for president in this state, and facing stiff competition from rivals who right now are ahead of him in the polls.

I sat down with him this afternoon to talk about the challenges he faces.

Vice President Joe Biden, thank you very much for talking with us.