DENVER – In a sign of mounting concerns among the party establishment about former Gov. John Hickenlooper's standing in the Colorado Democratic Senate primary, a new political group is spending at least $1 million on a scathing attack ad against Hickenlooper's rival in the race.The ad slams former Colorado House Speaker Andrew Romanoff for spearheading a package of tough bills opposing illegal immigration in 2006 that the ad calls “the nation's toughest anti-immigrant laws.” Romanoff has long since apologized for the measures.Romanoff is the underdog in the June 30 primary, running as a populist insurgent against the establishment's choice, Hickenlooper, who has raised significantly more money.