Compared to middle-class friendly changes like increasing the child tax credit and reducing payroll taxes, the top income tax rate should be at the bottom of Republican priorities. (It's not, but this is an argument that shouldn't be abandoned). Reihan writes at National Review:

Recently, I’ve been suggesting that Republicans ought to counter the president’s call for eliminating various tax expenditures to increase tax revenues beyond the levels reached under ATRA, AKA the fiscal cliff deal, by suggesting that we apply the revenue from the elimination of tax expenditures to an expanded child credit that could be used to offset payroll taxes, a la the Stein plan. This would leave the top rate under ATRA untouched while shifting the terms of the tax debate to friendlier terrain. Granted, this isn’t a consensus view among Republicans, but I think realism demands that conservatives recognize that for now at least, the political case for reducing the top marginal tax rate is relatively weak.

We aren't getting a top rate tax cut without a Republican in the White House, and we aren't getting a Republican in the White House without policies that broadly benefit the middle class. Whether elected Republicans recognize this is another matter, but for now, there are far more important concerns than the top marginal tax rate for our nation's best off.