Tax law changes

Great question! 

What you are referring to is called Unreimbursed Partnership Expenses. A partner in a partnership who has to pay expenses for the partnership's business and is not reimbursed for those expenses may be able to deduct those expenses on their personal tax return on Schedule E. This link describes how to enter these expenses in TurboTax:

https://ttlc.intuit.com/turbotax-support/en-us/help-article/partnership/deduct-unreimbursed-partners...

Vehicle expenses as you described can be an example of Unreimbursed Partnership Expenses. Please note, if your husband uses a standard mileage deduction, this is practically all-encompassing of other vehicle expenses such as repairs, gas, tires, oil changes, etc. He does not get to deduct standard mileage plus those other items. The only items which could be separately deducted, in addition to standard mileage, would be parking and tolls. 

If your husband wanted to use "actual expenses" instead of mileage, he would need to track all expenses for the vehicle such as gas, repairs, oil changes, etc. and in this case he could take a depreciation deduction to recover the cost of the vehicle. 

The IRS requires you to use either the standard mileage or actual expense method, for vehicle expenses in a particular year. You cannot combine them both for the same tax year. If you use the standard mileage method in the first year you place the car in service for business, then you can choose in each later year to either continue using standard mileage or switch to actual expenses for that year. If you use actual expenses in the first year, you must use actual expenses for that vehicle the entire time you own it. 

Here is a good IRS link about vehicle expenses. 

I hope this was helpful!