Cross-posted at ClickZ.

Republican Presidential candidate Mitt Romney was back online in a big way last month, aiming to rally supporters and establish a platform of popular conservative issues like government spending and border security. Romney For President ran over 22 million Web ad impressions in September, according to Nielsen/NetRatings AdRelevance. Meanwhile, perennial online advertiser John McCain 2008 reduced its display ad impressions from 191,000 in August to 25,000 impressions in September.

John McCain 2008 has gone from running millions of ads and multiple creatives in previous months to honing in on one main "No Surrender" slogan in September, intended to exhibit the candidate's unwavering stance on the War in Iraq.

According to the AdRelevance data, Romney For President ran Web ads in May and June, but took a break in the summer months. As the McCain campaign did earlier in the primary season, the Romney campaign appears to be testing various messages and ad formats. It experimented with standard display formats and expandable PointRoll units in the spring, but dropped the rich media in September, sticking with simpler animated units.

The Romney camp also introduced new messages, urging people to "Join the Rally," and recognizing grassroots support helping the campaign in Iowa.

Top sites for McCain ads included National Review Online, Dictionary.com, and conservative news site Newsmax. Romney ads also appeared on Newsmax, in addition to BellSouth's ISP site, FanFiction.net, iWon, FoxNews.com, and on New York Times Business, Sports and International site sections.

AdRelevance did not detect ads from any other presidential campaigns in September.

Note: Data were not available regarding sites where specific Romney For President ads ran.