Article Six of the U.S. Constitution specifically states that, '...no religious test shall ever be required as a qualification to any office or public trust'".
So the Democrats have created a scenario where the constitution is being violated, and Roberts has to play into their hands?
Asking him if his religious views will inform his decisions does not violate Article VI. In fact, the whole reason for Article VI was that it was assumed that particular sectarian views should not affect how an officer does his job. It was for that reason that they felt that discrimination on that basis was unjustifiable.