Did you hear the one about...? Okay, it's not that funny, but the Washington Post tells us that the Republicans are now considering a 21 percent corporate tax rate instead of the 20 percent rate that was in the bill passed by both the House and Senate.

The reason this matters is that the Republicans are assuming their tax bill will lead to additional growth, which they claim means $1.5 trillion in new revenue over the next decade. While virtually no economists outside of the administration accept this claim (the Joint Tax Committee assumes one third of this growth effect), the ostensible basis for the claim is the incentive for new investment based on a 20 percent corporate tax rate.

The problem here is that a 21 percent corporate tax rate means less of a reduction in taxes than a 20 percent corporate tax rate. This means it should provide less incentive to invest and a smaller increment to growth and revenue. But apparently, the Republicans don't intend to change their $1.5 trillion target implicitly leaving their growth assumption unchanged even though they've changed the basis for the assumption.

Welcome to the modern Republican Party: Up is Down, Night Is Day, and American is Great Again.