It's well known that Americans often equate the British accent with sophistication and class, until the Americans have been exposed to the yobs and wankers of the British thug culture. This has been confirmed by science. Imagine someone in your history class saying: "was Wellington named after the boot, or vice versa?" With a flat, midwestern accent, you'd be likely to say "silence, fool, while adults are talking!" but with a cultured British accent--and maybe a smattering of "I say!" and "how droll"--it's suddenly seen that the question was intended as wit. And while a Texan yelling at a hippie would sound crass--"up yours, longhair!"--there's something about the British version--"sod off, swampy!"--that just seems to belong in Masterpiece Theater.
About a half century ago it was even common for upper-crust east coast Americans to "Anglicize" their own accents, giving them that insufferable Thurston Howell hybrid that always makes it seem like they're talking down to the help. (Katherine Hepburn and FDR were good examples of this accent). And think about it--despite acting in an offensively stupid movie ("Guess Who's Coming to Dinner"), Hepburn was able to charm the Motion Picture Academy into giving her "Best Actress" for that farce. And despite some majorly stupid moves (putting Japanese Americans in concentration camps without due process, insisting on "unconditional surrender" for the Axis, selling out half of Europe to Stalin), FDR is not today referred to as the Goober Pyle of presidents. The accent is the key.
So what is my unsolicited advice for presidential candidates in need of image help?
1) Mitt Romney--already seen as a rich guy, should "Texan-ize" his accent, a la George Bush Sr.
2) Michele Bachmann--drop the midwestern accent, since no one ever says "he's from Michigan so he must be smart". Go with a British aristocrat accent.
3) Rick Santorum--go with California Surfer Boy (think, Keanu Reeves). They'll think you're more laid back and personable.
4) Tim Pawlenty--give yourself a Mexican accent. Hell, it can't hurt at this point.