When you are completing the MT state portion of the return, you will come to a series of questions asking about itemized deductions. First, the program will ask you if you itemized in 2016 and then you should get the screen below entitled "Montana Itemized Deductions - Schedule III" (see screenshot 1). You will need to click inside this form and scroll down on the Schedule III until you get to line 27 for Political contributions (limited to $100 per taxpayer). You will then need to make the manual entry of the amount next to each taxpayer.
If you don't get the below screens, you may instead get a screen informing you that you need to enter more itemized deductions in the Federal portion of the program before you will reach the threshold to itemize for Montana.
This did not work on the online version of TurboTax Premier. I spent over a half hour with on line help and they could not help me find the place to put in the 100 dollars per taxpayer--I did have plenty of other federal deductions (charity etc) to get to the Montana threshold for deductions, so that is not the problem. I've been using TurboTax for over ten years (only 5 years in MT) but I have not tried to deduct political contributions before--but if I can't find where to do it, I think the problem is with the program.
A few years ago they did not have a prompt for the MT specific light vehicle registration deduction, and now that has been corrected. They should have a prompt for the MT specific political contribution deduction!