The statement that the evidence BEST supports as an explanation for President Clinton’s popularity reaching its highest point immediately after his impeachment is:
A. President Clinton’s already high popularity led the public to disapprove of the impeachment.
This option aligns well with the data presented, as President Clinton's approval rating increased to 73% immediately after the impeachment proceedings began, suggesting that the public may have rallied behind him in response to the impeachment, leading to higher approval ratings.