A) Bush v. Gore (2000) CORRECT This is the correct answer because the case directly involved the counting of popular votes in Florida during the 2000 presidential election. The Supreme Court's decision halted the recount, citing equal protection violations due to inconsistent standards. This case is a prime example of the Court's involvement in electoral disputes and its interpretation of constitutional principles in the context of presidential elections.
B) U.S. v. Nixon (1974) INCORRECT This case concerned President Nixon's claim of executive privilege to withhold tape recordings and documents subpoenaed in the Watergate scandal. The Supreme Court unanimously ruled that executive privilege is not absolute and that the need for evidence in a criminal trial outweighed the President's claim. While it is a landmark case on presidential power, it has no relation to the counting of popular votes for president and vice president.
C) Baker v. Carr (1962) INCORRECT This case addressed legislative apportionment, specifically whether federal courts could hear cases challenging the malapportionment of state legislative districts. The Supreme Court ruled that such cases were justiciable under the Equal Protection Clause, establishing the principle of 'one person, one vote.' While it deals with voting rights and representation, it does not concern the counting of popular votes in presidential elections.
D) Citizens United v. Federal Election Commission (2010) INCORRECT This case involved campaign finance, specifically whether the government could restrict independent political expenditures by corporations and unions. The Supreme Court ruled that such restrictions violated the First Amendment right to free speech, leading to the creation of Super PACs. While it affects the electoral process, it does not address the counting of popular votes for president and vice president.