Impeachment or shutdown? Which bait to cast?

The conventional wisdom posits that Obama will hold off on his executive order granting legal residency to millions of Bush-era undocumented peon workers until after the midterms, to both minimize any negative impact on the elections for Democrats, and then bait the Republicans into disastrous impeachment talk ahead of JEB!'s expected early 2015 rollout, and the wind up to 2016.

The conventional wisdom is now under attack by left wing media (such as PMSNBC) where the current talking points support a much earlier (perhaps with a couple of weeks even) announcement designed to bait angry tea party members in Congress into forcing their leaders to shutdown the government in protest just prior to the midterms.  According to the logic, this will sour the public against Republicans and give Democrats a chance to hold onto the Senate.  There are a lot of big "ifs" in such logic, not the least of which is the GOP leadership, both House and Senate, unambiguously declaring "no way" they will allow the base to shut down the government before the elections.  Can they control their sheep this time?  The answer is probably yes, so the original plan of holding off until after the midterms is likely to do the most damage to the GOP brand over the next two years, as the nativist base then roars for months without Establishment support while "open borders" JEB! buys the nomination.