The Democrats have not provided a clear answer to this question: should a warrant be required to monitor an international phone call between a known foreign terrorist and a U.S. citizen who may or may not be suspected of terrorist ties?
No.
You said no, but the Democratic leadership characterizes this as "domestic spying on U.S. citizens" and opposes it (I believe, they have not been clear).
Is there evidence that anything other than this occurred?
Everything is kept secret, in part that was a big reason why the FISA regulations were set in place. After such "terrorists" like Martin Luther King JR were wiretapped with no warrants, but the kicker that led to the FISA law in part was Nixon's illegal taps. Bottom line no one is above the law. Their is no need to play fast & loose (or worse) with the wiretaps when it can be doone very easily in a legit & legal manner through FISA.
By the way some Republicans have voiced their concerns over the issue. Specter is taking a wait & see approach, but wants a full investigation, I believe Snowe, Collins, Hagel & I believe Chaffee at echoed similar things & Former NJ Govenor & Republican Chair on the the 9/11 Commission has commented on his worries about the program citing a need for "checks and balances" at all times. While supporting the taps Powell has questioned the need for bypassing the FISA regulations, stating that whhile he supports the taps & feels its important it should be done through a court order.