I believe the answer lies due to the increasing saliency among the electorate of social issues and moral values
And race. Okay, especially race.
Reactionary means wanting to restore an already gone past. Given that Roe vs Wade was thirty years ago, pro-life is technically reactionary...or maybe it's actually modern, but it surely is not technically a conservative position.
I'd assume Sirota is referring mostly to people who're leftist economically as well as socially - not people as described in the next sentence:
Of course, the reasons why that makes sense are obvious.
In what sense? (I'll leave the whole international perspective out for the moment, it confuses or perhaps clarifies matters further.)