Here’s what their latest editorial has to say about the constitutional question:

[T]he legislation, as it’s crafted, addresses these concerns–since it provides for expedited judicial review of the bill if it’s challenged after becoming law. As Republican Senator Susan Collins of Maine said in voting for the bill in committee last week, “I have concluded that the constitutionality of this legislation is a close call and is best resolved by the courts and not by this committee.”
Which means that something else may be behind Bush’s and McConnell’s continued opposition to the legislation.

Well, if in Susan Collins’s finely honed legal mind it’s a close question, then it must be, right?