I suspect that Michelle Bachmann will not get the GOP presidential nomination but the attempt to slam her as anti-Catholic because of her membership in the Wisconsin Evangelical Lutheran Synod is pure politics.
To be sure, WELS - as an institution - takes a rather harsh view of the Papacy. But it's not clear to me that most congregants take much heed of that or that, to the extent they do, that church doctrine concerning the papacy translates into any particular attitude about Catholics that affects one's relationship with people and groups that are Catholic. My brother-in-law, for example, is a member of WELS. You'll have a hard time finding a better guy.
I might be more impressed by the matter if so many Democrats weren't perfectly willing to absolve Democrats of belonging to churches with what they consider to be objectionable doctrine. For example, the Catholic Church teaches that homosexuality is intrinsically disordered and that abortion is murder. Yet Democrats seem perfectly able to understand that a politician - such as Joe Biden, Nancy Pelosi or John Kerry - may belong to the Church and not share those views. Barack Obama belonged to a church headed by a race baiting, conspiracy mongering nut who he claimed was some form of father figure and transformational influence in his life, yet his supporters were perfectly able to distinguish the President from Reverend Wright.
In fact, when it comes to Democrats criticizing others for being anti-Catholic, recognition of a certain degree of irony is in order. Many on the left believe that being pro-life is to be "anti-woman" or that opposing same sex marriage is bigotry. These are, of course, attacks on faithful Catholics in a way that WELS rejection of the papacy is not. In other words, the left wants to hang Bachmann for being an anti-Catholic bigot for belonging to a church that takes a theological position she has repudiated, while it argues that Catholics who follow the teaching of the Church are immoral.
If that doesn't persuade you that the criticism of Bachmann for her former membership in WELS is cynical political posturing, please direct me to the criticism of Democratic politicians who belong to the WELS. We needn't go far to find one. How about Ron Kind (D-Wis.)?