Franklin Roosevelt, Ronald Reagan and Bill Clinton all understood that Americans prefer hope and optimism to gloomy declarations of impending doom. Why would Romney and so many in his party want to be the doom guys?
If I may, E.J. (And this is just a gentle reminder, since I know you already know this, and indeed you vaguely touched on it: "Romney’s problem is that he is caught in a cycle he can’t seem to escape ... [his] ongoing problems with the right wing of the Republican Party.")
"Why would Romney and so many in his party want to be the doom guys?" Because Romney et al must answer to the rank-and-file doom guys, the nihilistic GOP base, which, with alarming progression, is morphing collectively into an 'Authoritarian Personality,' as delineated in 1950 by Theodor Adorno et al.
Their study's key sociopolitical finding: Fear and destructiveness lie at the heart of the extreme right-wing personality -- a personality stubbornly impenetrable and perhaps immutable. That is, one cannot appeal to its rationality, for much of its fear stems from a hatred of ethnics and "others," a fear that is intrinsically irrational; and one cannot appeal to what Dionne exhorts -- attitudinal "hope and optimism" -- for the authoritarian's symptomatic exaltation of patriotism is in deeper, and paradoxical, reality a violent impulse to destroy positive government.
In short, right-wing extremists are essentially anarchistic -- yearners, we might say, for a primitive, lawless, Hobbesian state of nature.
A few seconds viewing any videotaped tea party rally is easy but profound confirmation of Adorno's insights.
Authoritarian personalities? The "right wing of the Republican Party"? -- i.e., the contemporary Republican Party? Yep, they're the "doom guys."