The point is that free trade is politically viable only if it's backed by effective job creation measures and a strong domestic social safety net.
Economists argue about a lot of things, but the benefits of trade are to economics as natural selection is to biology. Krugman defends free trade as he must and should.
Economists do fight about how best to help the "losers" free trade produces. Conservatives favor tax cuts, liberals favor training and unemployment insurance. That's a legitimate fight. I favor 529 plans to cover living costs when unemployed and retraining with mandatory contributions when employed. That's a policy many Republicans would accept.
Where Republicans are vulnerable is health care and benefits. These need to be removed from employment. Krugman is starting to talk about this. It's a winner for Kerry.