Pope Benedict has made it very clear that he wants to turn back the clock on several matters of church policy and politics. He is backing away from many of the Vatican II reforms. He is aggressively competing with the Anglican communion for priests and parishioners. The Catholic Church in the United States also seems more aggressive in its involvement with secular politics than at any time in the recent past.
The Catholic Church partnered with the LDS Church in a campaign to promote California's Proposition 8. It has brought pressure to bear on Washington, D.C. regarding recognition of same-sex marriage (threatening to close down its charitable service organizations in the District if they are not allowed to discriminate against homosexuals). It is actively opposing health care reform legislation unless it includes abortion restrictions (effectively saying that everyone, regardless of their own religious beliefs, should be forced to live according to the dictates of Roman Catholic doctrine).
Whether or not you think it is a right and proper thing for the church (any church) to get involved with politics is a matter of subjective belief. Right now, I am more interested in the tactics the RC Church is using, and the other tools that Pope Benedict may choose to deploy.
The Bishop of Rhode Island has banned Rep. Patrick Kennedy from receiving communion because of his support for abortion rights. Note that Kennedy is not an abortion provider, nor is he accused of procuring an abortion for someone else, or encouraging anyone to have an abortion. He is being punished by his church because he does not support the notion of secular law enforcing church doctrine.
Kennedy is not the first politician to be denied communion for supporting abortion rights. I find it interesting, however, that the RC Church has not withheld communion from politicians for supporting the death penalty (also contrary to RC doctrine) or the elective invasion of Iraq (which caused the death of many innocents).
Thus far, politicians have not been swayed by this tactic. I have not heard of any who have changed their positions in order to get back in the good graces of the church. This may be because most Americans, even Catholics, are uncomfortable with the idea of the Papacy (which is, after all, a foreign government) giving marching orders to their elective officials.
Historically, however, the RC Church had a much more powerful weapon to use against rulers who defied Papal orders. A local interdict was sometimes imposed against an entire jurisdiction -- banning the sacraments and effectively excommunicating everyone within its borders -- until the leader bowed to the Papal will.
It hasn't been used since the days of the counter-reformation (perhaps because the RC Church was afraid to lose market share to the Protestants). However, Pope Benedict has shown himself willing to preside over a smaller but purer flock. Will he go so far one day as to place Kennedy's Congressional District under interdict until he is voted out of office?
Time will tell.