Oh I don’t think the democrats are worried - if an establishment squish gets the nomination the worst they’ll get from the republicans are expressions of “concern”.
Repubs already gave in when they agreed that it would take 60 votes to over-ride the treaty, instead of following the constitution where it requires two-thirds vote to approve it.
Boehner is a fraud, and so are most of the Repubs in office. This similar to the TPP, where they have agreed in advance the same thing, it takes a super-majority to override rather than requiring a super-majority to approve.
Frauds, every one of them.