Called today but did not leave a message.

This is a call from a pac (Keep The Promise III), which represents Ted Cruz. Just another robo call for a politician.
Don't bother to answer. You can always be sure, if the phone stops ringing after three rings, it is most likely a robo scammer. If people are calling, not machine, they will wait longer to give you a chance to answer.

Won't leave a message. Won't identify themselves. Reported as political robocall in other comments.

Calls several times a day, but does not leave message.

Total of 7 calls over past 3 days from this number. Doesn't leave a message.