Portman, Rubio, possible GOP VP, unknown

PRINCETON, N.J., June 20 (UPI) -- Less than half of Americans know enough about two possible Republican vice presidential candidates to form an opinion about them, a poll indicated Wednesday.

Of the two, U.S Sen. Marco Rubio is viewed more favorably than unfavorably while views on Sen. Rob Portman of Ohio were mixed, results from a USA Today-Gallup poll indicated

Presumptive GOP presidential nominee Mitt Romney hasn't indicated who's on his list of possible running mates.

Forty-four percent of Americans in a May 7-10 USA Today-Gallup poll said they could give an opinion of Rubio, compared with 22 percent of Americans who said they have an opinion about Portman.

Results for the latest USA Today-Gallup poll are based on nationwide telephone interviews with 1,012 adults conducted May 10-13. The margin of error is 4 percentage points.