GREENVILLE, N.C. -- Republican vice presidential candidate Sarah Palin says Barack Obama's association with a 1960s radical is a relevant issue because he hasn't been forthright about what he knew about William Ayers' background and when he knew it.

Palin says raising Ayers, a founder of the violent Weather Underground, speaks to Obama's ability to tell the truth.

The Alaska governor spoke with reporters between campaign appearances Tuesday and said that if Obama can't be straight about Ayers, how can voters believe what he tells them about taxes or other issues.

Ayers helped found the Weather Underground, whose members were blamed for several bombings when Obama was a child.

Obama has denounced Ayers' radical views and activities.