If Congress and President Obama are ever going to get serious about tax reform, they will have to rethink some of the biggest and most popular tax breaks. It won’t be easy. Those tax breaks mostly benefit powerful voting blocs: the middle-class and the wealthy. The federal government gives up $1 trillion in revenue every year because of the hundreds of tax credits, deductions, exemptions and exclusions in the tax code. And the top 10 account for most of that $1 trillion. (Table of Top 10 below.)