A clash of faiths in the U.S. Senate last week led to the collapse of the country’s first major immigration reform bill in two decades. On one side were the pragmatists, backed by the Bush administration, who say the country needs to accept that its estimated 12 million illegal residents are likely here to stay, and it should offer them a path to citizenship. On the other side were the idealists, who say lawbreakers shouldn’t be rewarded, and that doing so would only encourage more illegal immigration. Although Democratic majority leader Harry Reid withdrew the bill, he left open the possibility that the Senate could reconsider it later in the year. President Bush, having just returned from the G8 Summit in Europe, made a rare appearance on Capitol Hill this week to encourage Republicans to back the proposal.    Buried in the ongoing debate is the potential economic impact of a measure that could change the composition of America’s workforce in significant ways.…