This week could turn out to be a moment of truth for those who have spearheaded the backlash against illegal immigration to the US.

For a nation that was - and continues to be - built on immigration, the debate has so far proved very un-American. Politicians from both parties have joined forces with talk-radio celebrities and vigilante patrol groups to demand a 700-mile fence along a large section of the Mexican border. Bill Frist, the Republican Senate leader and a 2008 presidential hopeful, has drafted a bill that would criminalise the estimated 11m illegal immigrants in the US. And Lou Dobbs, the populist CNN anchorman, frightens Americans every night with the spectre of a low-wage Hispanicised future.