“As you start walking members through that, there’s a realization that this isn’t just some flip throwaway,” he said. “I really do believe members make their decisions more based on their districts than on what’s personally best for them.”

In Jeopardy

The break is in more jeopardy than at any time in the 27 years since Congress last revamped the tax code.

Baucus, who doesn’t have a mortgage on his family’s home in Montana, wants lawmakers to examine every tax break and is asking senators to make suggestions by July 26.

“Every provision we put back in the code needs to have a reason for being there,” he said in a statement.

This is the second year that lawmakers have required themselves to disclose the terms of their mortgages, a demand prompted in part by reports that Countrywide Financial Corp. had a “Friends of Angelo” program named for co-founder Angelo Mozilo that offered below-market rates to politicians.

Members of Congress must report mortgages on any property they own, regardless of whether it produces income. They must report only the value of homes that generate income, which means that those who own their second homes outright and don’t rent them don’t have to disclose them.

Tax Returns

The lawmakers also don’t have to disclose their tax returns, making it impossible to know how much any of them benefit from the break.

Of the 63 members of the Ways and Means and Finance committees, 26 report mortgages on second homes, mostly in the Washington area. All except six members have filed forms covering 2012 that were due May 15; the others received extensions of the deadline.