taxable period
(4) Taxable period The term “taxable period” means, with respect to any political expenditure, the period beginning with the date on which the political expenditure occurs and ending on the earlier of— (A) the date of mailing a notice of deficiency under section 6212 with respect to the tax imposed by subsection (a)(1), or (B) the date on which tax imposed by subsection (a)(1) is assessed.