If there were a gold medal for political use of new technology, almost every web aficionado would award it to Barack Obama. But on Thursday Mr Obama provided a reminder that what has already been dubbed the “YouTube election” can also be a double-edged sword.

Launching a site called “Fight The Smears”, Mr Obama’s campaign abandoned its policy of ignoring the most lurid internet rumours about its candidate. Of these, the most recent was the widely e-mailed contention that Karl Rove, the legendary Republican operative, possessed a tape of Michelle Obama railing against “whiteys” in a race-infused speech at the church formerly run by the provocative pastor Jeremiah Wright.