Things get very complicated here IF the husband wants to make a deductible spousal contribution from wife's income, since he is also receiving SS benefits.
This triggers Appendix B worksheets in Pub 590, all 3 of them. Basically, since modified AGI is determined by and ALSO effects both the TIRA deduction and taxable SS benefits, the worksheets use an articial MAGI calculation (WS 1), use that MAGI to determine how much of the TIRA contribution can be deducted (WS 2), and then use that TIRA deduction to determine MAGI for SS benefit taxation (WS 3). WS 3 replaces the usual SS taxation worksheet normally used.
If WS 2 limits the deduction, the non deductible portion should either not be made OR should be made as a Roth contribution instead.