This headline in NY Times gives a clue:
Then later in the story:
Guantánamo Thorny Issue for Democrats on Committee
...Apparently some have learned what Durbin learned the hardway. In a debate over treatment of the enemy, it is not a good idea to be on the side of the enemy.
For Republicans, the mission was simple and direct: defend the military's detention center at Guantánamo as humane and deserving of admiration throughout the world.
For some Democrats, the task was more complicated: to praise the patriotism and work of the vast majority of military personnel at Guantánamo, while raising questions about abuse of detainees.