The assumptions that lead to this being the optimal tax rate are based on the US experience: that people cannot simply leave the country to escape high income tax.

FORBES: Eurozone: Why The Austerity Solution Is Doomed To Failure

But what we simply cannot allow is Republicans to take care of the spending bill and leave town because the absolute effect of that would be a tax hike for middle-class Americans.

WHITEHOUSE: Press Briefing