WASHINGTON — The federal government is on track to reopen, but that doesn’t mean the political pressure is off U.S. Sens. Michael Bennet and Cory Gardner of Colorado. Several activist groups took aim at the two lawmakers after they voted to end a three-day government shutdown that many advocates saw as their best chance to force action on immigration reform — particularly for the hundreds of thousands of immigrants sometimes called Dreamers, who were brought illegally to the U.S.