Might as well have them swear in on something they believe in, not that the left upholds their oath to uphold and support the Constitution anyhow.
Honestly, I'd rather politicians lay their hands on a copy of the Constitution and Bill of Rights. Even better, line them up at the National Archives and lay their hands over the glass protected actual documents themselves. Then make them fucking read every last word out loud and swear upon their life to not violate it, punishable by old school tar and feather followed by the gallows if they do.