Previewing tonight's vice presidential debate in a conference call with reporters, members of President Obama's campaign staff suggested Rep. Paul Ryan will distort the facts. 

"Joe Biden, as he always does, will speak the truth," campaign manager Jim Messina said, while Ryan, "from his fact-free convention speech to his exaggerated marathon time ... isn't afraid to stretch the truth." 

The campaign also sought to shift some emphasis away from debates and towards the ground game, pointing to leads over Republicans in battleground state voter registration. 

"You can't fake a good ground game," said Jeremy Bird, the campaign's national field director. "And if you don't have one you cant compensate with a barrage of ads at the eleventh hour." 

Ryan himself noted in an interview earlier this week that Democrats would accuse him and Mitt Romney of lying. “They’re just going to call us liars for a month," he told radio host Frank Beckmann.