While I'm sure the GOP leadership isn't thinking "let's tank the economy," I'm also sure that for the past four years they've been thinking: "If we pass x, y, and z it will help the economy which will help Obama's re-elect, so we have to block any legislation that helps his re-elect."
Of course, they're the same thing - destroying the economy and stopping Obama from being re-elected - but in politics, it's all too easy to make a disconnect between the two, and thus Republicans can hold themselves harmless for a very real, and effective, four-year strategy to harm the American economy.
From Michael Cohen in the Guardian:
Beyond McConnell's words, though, there is circumstantial evidence to make the case. Republicans have opposed a lion's share of stimulus measures that once they supported, such as a payroll tax break, which they grudgingly embraced earlier this year. Even unemployment insurance, a relatively uncontroversial tool for helping those in an economic downturn, has been consistently held up by Republicans or used as a bargaining chip for more tax cuts. Ten years ago, prominent conservatives were loudly making the case for fiscal stimulus to get the economy going; today, they treat such ideas like they're the plague.
Traditionally, during economic recessions, Republicans have been supportive of loose monetary policy. Not this time. Rather, Republicans have upbraided Ben Bernanke, head of the Federal Reserve, for even considering policies that focus on growing the economy and creating jobs.
And then, there is the fact that since the original stimulus bill passed in February of 2009, Republicans have made practically no effort to draft comprehensive job creation legislation. Instead, they continue to pursue austerity policies, which reams of historical data suggest harms economic recovery and does little to create jobs. In fact, since taking control of the House of Representatives in 2011, Republicans have proposed hardly a single major jobs bill that didn't revolve, in some way, around their one-stop solution for all the nation's economic problems: more tax cuts.