GOP leaders will pursue tax reform under special budget "reconciliation" rules preventing a Senate Democratic filibuster. But that requires two things that won't be easy: passing a budget and keeping at least 50 of 52 Senate Republicans united behind the tax plan.
Republican moderates such as Sens. Susan Collins and Lisa Murkowski, who helped sink Obamacare repeal plans, will scrutinize the tax proposal as well on fairness and fiscal-responsibility grounds. And the populist insurgency that rattled GOP leaders in this week's Alabama Senate runoff adds another wild card.
Before resigning as Trump's White House strategist, Steve Bannon argued unsuccessfully for raising the top rate on wealthy Americans to 44 percent. Now back at Breitbart News, Bannon vows to battle more "establishment" Republicans on behalf of blue-collar voters as he did in boosting Roy Moore's defeat of Alabama Sen. Luther Strange.
Bannon-allied primary challengers to other GOP incumbents could affect the Senate debate by pressing for a higher top rate. That in turn could roil the House, where Speaker Paul Ryan has staunchly favored lowering marginal rates.