It's time for the American center-left to put up, or shut up.

If global free trade has been a boon to America, then prove it: systematically with cold hard facts and logic.

If liberalized  immigration and embracement of multiculturalism is such an overwhelming benefit, then again, prove it.

I believe that the first premise would be easy to prove, the second one, probably not. In fact, I believe efforts to prove the second premise would actually disprove it.

And therein lies the rub: liberals may have to abandon one of their  sacred cow core principles to regain power.

Better get to work, because the next election cycle started 2 days ago.