A $17,000 cap -- which would raise the most revenue and hurt the rich the most, since they benefit disproportionately from deductions -- might bring in $1.7 trillion over a decade, or $170 billion a year, the Tax Policy Center estimates.

That's a little higher than the $150 billion that the CRS estimated might be plausible to raise. But not much.

In either case, lawmakers wouldn't be swimming in additional revenue as they try to both reduce deficits and lower rates.