The current Democratic bet is three fold. The first is that there will be an internal Republican civil war that will cost the GOP numerous winning opportunities. The prime example would be the NY-23 special election as the Teabagger+GOP vote was greater than the Democratic vote, but the Democrats won anyways. The second is that the GOP is still fundamentally discredited and most swingable voters would be pinching their noses with three ton vises to vote for the GOP.
Finally, the Democratsa are making a bet that they bad policy that they ares supporting is “good policy” for the swing money. And they expect to see the swing money continue to back the Democrats which will be enough to either depress GOP turnout or get enough apathetic Democrats to turnout to hold a decent size majority next year.
I agree : they are betting that they are lesser of two evils, the Republicans are borked beyond saving for at least another couple years and that the money they make through bad policy (aka: seeing to the interests of the rich rather than the majority of the population) is sufficient to make up for the negative electoral effects of those policies.