Can I carry forward investment interest (from a prior year) that would be deductible this year, until next year?

[Anita01]

No, investment expenses, including interest, can no longer be deducted because Miscellaneous itemized expenses are no longer deductible under the new tax rules.

[techtownhomes]

This answer is NOT correct.  Investment interest expense is not a miscellaneous deduction, it is an interest deduction.  It IS deductible as an interest expense for 2018 taxes.

[SweetieJean]

If you itemize your deductions, you may be able to claim a deduction for your investment interest expenses. Investment interest expense is the interest paid on money borrowed to purchase taxable investments. This would include margin loans you use to buy stock in your brokerage account. In such cases, you can deduct the interest on the margin loan. (This wouldn’t apply if you used the loan to buy tax-advantaged investments such as municipal bonds.)
The amount that you can deduct in a given year is capped at your net taxable investment income for the year. Any leftover interest expense gets carried forward to the next year and potentially can be used to reduce taxes in the future.
However, I do not believe that you can select to carry it over rather than use it,

[techtownhomes]

Thanks, I assumed that the IRS will not allow you to pick what year to use carried over deduction. Thx for you thoughts on it as well.