Speaking as private citizen, he called Obama the "most committed" abortion rights candidate since Roe vs. Wade (in other words, ever). Among other comments, Archbishop Chaput said:
"I think [a Catholic law professor's] activism for Senator Barack Obama, and the work of Democratic-friendly groups like Catholics United and Catholics in Alliance for the Common Good, have done a disservice to the church, confused the natural priorities of Catholic social teaching, undermined the progress pro-lifers have made, and provided an excuse for some Catholics to abandon the abortion issue instead of fighting within their parties and at the ballot box to protect the unborn."
And he also called out the pro-Obama "what about poverty and war?" Catholic liberals, noting that they "seek to contextualize, demote and then counterbalance the evil of abortion with other important but less foundational social issues."
Look, it's a free country and Catholics obviously have the right to ignore the Archbishop. But they sure can't say that they did so because they didn't have guidance or teaching from the Church.