More than just a feeling. He has folded on key issues and the republican "establishment' considers him their go to guy if Jeb is booted or quits.
He was on the Senate committee that ceded their treaty approval power to Obama concerning Iran. He voted to give up their authority.
Indications are that, when push comes to shove, he will always side with the "establishment" and against conservatives.
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"The unmistakable gaping hole in Rubio’s conservative record is his active and prominent voice for amnesty and comprehensive open borders. When judging a member’s work in the broader conservative cause, dissension on one issue would not taint their entire record. But in the case of Rubio and immigration, due to the importance of the issue and
the fact that he carried the amnesty bill on his shoulders, even after his own promises were proven wrong, has severely strained his relationship with the grassroots. Conservatives feel as if Rubio didn’t just work across the aisle, but delivered the votes needed across the aisle for liberal Senator Chuck Schumer and the open borders movement against the center-right rule- of- law coalition. Aside for immigration, Rubio has a weak spot for some aspects of the populist fiscal agenda that are not inherently conservative. While his strong position against corporate welfare overlaps with the conservative agenda,
parts of his anti-poverty agenda are not built upon the foundation of free market and limited government principles. He opposes the requisite downsizing of government in order to balance the budget. He supports keeping the costly Obamacare mandates on pre-existing conditions, and he has supported government intervention in hiring employees and incentivizing wage increases." - See more at:
https://www.conservativereview.com/members/marco-rubio/#sthash.HjftQDv9.dpuf
"Senator Marco Rubio, newly declared for president, sits on the Senate Foreign Relations Committee. Where he voted for what Mark Levin accurately describes as an agreement that has “turned (the Constitution) on its head.” - See more at:
https://www.conservativereview.com/...or-stand-tall-under-fire#sthash.TmR4W7ME.dpuf