Senator Marco Rubio had a tax-reform plan that made him stand out from the Republican pack this primary season. He has apparently concluded that he stood out too far. The revised version he's now offering would still be a major improvement over current tax law in many respects. Unfortunately, it also makes his original plan's biggest drawback even worse.

Rubio's proposal follows a model Republicans have used for decades: combining supply-side tax-rate cuts with tax relief for middle-class families. Just like President George W. Bush, Rubio wants to reduce the top tax rate to 35 percent. But Rubio goes much further than Bush in cutting taxes on investment. He also goes further for middle-class families, expanding the child tax credit by $2,500 and letting parents use it to offset payroll taxes.

Not surprisingly, all this leads to lower revenue for the federal government. The Tax Foundation estimated that over the first 10 years that revenue reduction would amount to $6 trillion, unless the reform boosted economic growth. That's one of the bigger tax cuts on offer from Republicans in the 2016 campaign.

Read the full article at Bloomberg View: Marco Rubio's $6 Trillion Problem