I can understand your frustration with the relatively small number of Jews who vote Republican, because voting for 'Rats by anyone hurts the conservative movement in general. Even accepting your 20% number (which, of course, varies depending on the election and is usually underestimatated due to flaws in polling techniques by pro-'Rat pollsters), you will be surprised that come November that number will just about double in the presidential election, even granted that Romney is far from a true conservative.
Romney being a "true conservative" would hurt his share of the Jewish vote, not increase it.