A “Senate moderate” is someone who takes his party’s proposals, objects to them, waters them down a bit, and then congratulates himself on a job well done. Which is great if his party’s proposals are unduly immoderate. But it’s big-time trouble if his party puts a reasonable, moderate agenda on the table.
After all, you don’t maintain the painstakingly achieved Nelson/Bayh “Senate moderate” brand by clapping politely. You need to bitch and moan and be quoted in inside-baseball only media outlets that none of your constituents pay attention to, and hold conferences and have meetings at the White House where people hold your hands. You need to be praised by the opposition party, and extract your pound of flesh from the proposal. Then when it looks like it might go down to defeat, you can vote for the somewhat-watered-down version and be the hero who saved the day and nobody will mention that you saved the day from yourself.
But you really do need to do that stuff. You can’t just say “well, this is a reasonable proposal so I’ll back it.” Then your moderate license gets taken away.