It's both. He was calculating (incorrectly most likely) that he could alienate the anti-genocide part of the party as long as he made up those numbers with independents and conservatives and whoever else. But then his public display of mental collapse meant that he wasn't scraping together that critical support either, so his support is plummeting across the board.

Without the pressure from the anti-genocide coalition he might not have ended up in this situation, as most democrats are ready to compromise, just not on killing children.