I think he’s been reading the smoke signals and sees that there will be a Republican Tsunami in 2016. I think a lot of marginal Democrats will get swept out of office next year.
Remaining a Democrat in his district was the safe choice.
Begay is the one taking a risk - if his standing with his constituents is solid, he could remain in office as a Republican and that would be huge.
Check out the video linked in post # 8.
All long-held Democrat places should follow suit.