Josh Barro, here:
Currently, you get to take the personal exemption even if you also itemize deductions, but you get to take the standard deduction only if you forego itemized deductions. Combining these provisions into a single, standard deduction would mean itemizers lose their personal exemption and get nothing back — meaning they'll typically pay tax on an extra $4,050 of income if they're single, or $8,100 if they're married.
