COUNCIL BLUFFS, Iowa — As Mitt Romney caravans confidently across Iowa, he has been taking increasingly sharp digs at President Obama.

The Republican presidential candidate unleashed his latest here Sunday night, at once dismissing Obama as an empty man of false promises and showing off his own alleged pop culture know-how.

“You know, I’ve been looking at some video clips on YouTube of President Obama, then-candidate Obama, going through Iowa making promises,” Romney said as he rallied several hundred supporters in downtown Council Bluffs. “And I think the gap between his promises and his performance is the largest I’ve seen, well, since the Kardashian wedding and the promise: ’Til death do us part.’ ”

It was an unusual comment from a candidate often ridiculed for his lack of modern cultural awareness. Asked whether Romney came up with the line himself, his aides simply laughed — and, of course, they offered no answer.