When Mike Pyne and other union foot soldiers knock on doors to promote Senator Barack Obama, they often confront a tricky challenge: how to persuade union members to vote on the basis of their wallets rather than on issues like abortion, gun rights and race. In battleground states like this one, union voters could be vital to the outcome of the election, and the labor movement has mounted a huge push on behalf of Mr. Obama, the Democratic presidential nominee, built largely around the message that with unemployment rising, the financial system reeling and gasoline and food prices soaring, the nation cannot afford to have another Republican in the White House. continue reading