Not 20, and not 22?Actually I agree that, other things equal, a loss by the Democrats and a gain by the Republicans of about 10% of black voters would leave the Democrats flat on their back with truck tire tracks across their collective chest.
Even less than that would do it, if combined with either a large defection to a third party, or simply low turnout. But I would far prefer to see the Republican party getting doubled support from blacks, and deserving it. Most especially on the voucher issue.