Mitt Romney has been determined to resist releasing his tax returns at least since his bid for Massachusetts governor in 2002 and has been confident that he will never be forced to do so, several current and former Bain executives tell The Huffington Post. Had he thought otherwise, say the sources based on their longtime understanding of Romney, he never would have gone forward with his run for president.

Bain executives say they've been instructed to keep company and Romney-specific information completely confidential, tightening the lockdown on an already closed company.

But pressure has been building on the presumptive GOP nominee. On Tuesday, the conservative National Review added its voice to a chorus of Republicans pushing him to disclose his returns from the years before 2010.