The contrast could hardly be starker. One ad depicts former Republican Rep. Brian Bilbray heroically battling millions of gallons of invading Mexican sewage using a bulldozer. The other focuses on Democrat Francine Busby deadpanning about ethics and pledging to help clean up Washington.

And Bilbray’s bulldozer ad might well help him keep a Democrat from invading California’s 50th District House seat in June’s special election, according to a poll by Wilson Research Strategies.

Bilbray and Busby are locked in a battle for the seat, vacated by disgraced former Rep. Randy “Duke” Cunningham’s (R). The ads play to their campaign messages: Bilbray as a tough immigration hawk, Busby as an everyday woman who wants to stamp out the kind of corruption Cunningham embodied.

In a match-up of the two ads, 51 percent of political insiders found Bilbray’s border-security ad more effective than Busby’s ad, which consists of inanimate promises not to accept gifts or lobbyist-funded travel and not to engage in “secret pork-barrel spending.” Thirty-one percent of the respondents said Busby’s ad was more effective.

Bilbray’s ad opens with shots of a big bulldozer and the narrator, without providing context, talking about how, as a mayor, Bilbray “defied bureaucrats” by hopping onto a bulldozer to keep the “Tijuana sewage” off the district’s beaches. It then shows Bilbray shaking hands with Border Patrol and standing tough on the border, saying that, as a congressman, he added 1,400 Border Patrol agents. It wraps up with Bilbray saying border security “cannot wait another day.”

Busby’s ad is much blander and more straightforward. Minus a few nods of her head, the trucking camera is the only thing that moves. Still, she delivered a strong message on ethics. In the ad, she decries people using “corrupt money from Duke Cunningham and [outgoing Rep.] Tom DeLay [R-Texas] to attack me” and goes on to promise “real change in Washington” and an end to “politics as usual.”

People generally found Busby’s ad to be political advertising as usual. Those surveyed rated Bilbray’s ad a 5.7 for effectiveness on a scale of 1-10, with 10 being the highest. Busby’s received a 4.8. And while only 13 percent of Republicans found Busby’s ad more effective, 33 percent of Democrats said Bilbray’s was better.

Wilson Research Strategies CEO Chris Wilson said the visual appeal of Bilbray’s ad was clearly the difference-maker.

“The one [rating] that I really thought was most interesting was that Republicans rated Bilbray so much higher than Democrats did Busby,” Wilson said. “Across the board, Republicans are far more optimistic about this race than Democrats are.”

Bilbray’s ad scored better overall for the strength of its message, its appeal and its credibility and in the category “an ad I would talk about.” Bilbray’s ad was rated much more memorable.

Forty-one percent of the 400-plus respondents described themselves as Democrats and 33 percent were Republicans.

Working with The Hill for its Air War feature, Wilson Research Strategies e-mails campaign or issue ads to survey participants who view the ads and rate their effectiveness on several criteria.