There must have been tangible tension in the air at a lunchtime gathering on Tuesday, as Bernie Sanders and Hillary Clinton sat together for the Senate Democratic Caucus meeting. Rival candidates meet with each other all the time, so normally there wouldn’t be any oddities about a routine caucus meeting, but this particular encounter was more uncomfortable. Ms. Clinton has the backing of 30 Democratic Senators, to Sanders’s 0, and she has been playing the part of a presumed nominee well. Tip-toeing around divisive issues and falling into line with big-time donors, Ms. Clinton has performed all of the dull dances to perfection. But Sanders’s straight talk and unconventional – but righteous – campaign route has resulted in his evolving from an irritating nuisance to a significant pain in the neck of Hillary Clinton's campaign. It is Sanders’s surge that created the tension on Tuesday. Clinton seemed to throw a patronizing compliment at the Vermont Senator, praising the “enthusiasm his campaign has brought to the race.” Sanders immediately outlined his differences with Hillary following the meeting. While campaigning, Hillary has not yet mentioned Bernie Sanders by name, although she may soon find herself having to actually acknowledge her political rival.