"That's one of them. That's one of why we lost in part," the Democratic senator from Pennsylvania told Fox News.

The bill, which would require federal authorities to detain undocumented immigrants arrested for theft-related crimes, was the first to be voted on by the newly installed Republican-controlled Senate.

The Senate cleared the 60-vote threshold to begin debate on a GOP priority, with Democrats backing it as the party recalibrates politically on immigration. Final passage is still uncertain.