Question: Which of the  high-profile candidates vied for the Reform Party presidential primaries, 2000 was a senior advisor to U.S. Presidents Richard Nixon? 

Context paragraphs:
Donald Trump presidential campaign, 2000: Donald Trump's presidential campaign of 2000 for the nomination of the Reform Party began when real estate magnate Donald Trump of New York announced the creation of a presidential exploratory committee on the October 7, 1999 edition of "Larry King Live".  Though Trump had never held elected office, he was well known for his frequent comments on public affairs and business exploits as head of The Trump Organization.  He had previously considered a presidential run in 1988 as a Republican, but chose not to run.  For 2000, Minnesota Governor Jesse Ventura persuaded Trump to seek the presidential nomination of the Reform Party, which was fracturing despite achieving ballot access and qualifying for matching funds as a result of the 1996 presidential campaign of businessman Ross Perot.  Trump's entrance into the Reform Party race coincided with that of paleoconservative commentator Pat Buchanan, whom Trump attacked throughout the campaign as a "Hitler-lover."

Democratic Party presidential primaries, 2020: The 2020 Democratic Party presidential primaries and caucuses will be a series of electoral contests organized by the Democratic Party to select the 4,051 delegates to the Democratic National Convention and determine the nominee for President of the United States in the 2020 U.S. presidential election.  The elections will take place within all fifty U.S. states, the District of Columbia, and five U.S. territories.  An extra 716 unpledged delegates (712 votes) or "superdelegates", including party leaders and elected officials, were appointed by the party leadership independently of the primaries' electoral process.  The convention also approved the party's platform and vice-presidential nominee.

Pat Buchanan: Patrick Joseph Buchanan ( ; born November 2, 1938) is an American conservative political commentator, author, syndicated columnist, politician and broadcaster.  Buchanan was a senior advisor to U.S. Presidents Richard Nixon, Gerald Ford and Ronald Reagan, and was an original host on CNN's "Crossfire".  He sought the Republican presidential nomination in 1992 and 1996.  He ran on the Reform Party ticket in the 2000 presidential election.

Democratic Party presidential primaries, 2016: The 2016 Democratic Party presidential primaries and caucuses were a series of electoral contests organized by the Democratic Party to select the 4,051 delegates to the Democratic National Convention held July 25–28 and determine the nominee for President of the United States in the 2016 U.S. presidential election.  The elections took place within all fifty U.S. states, the District of Columbia, and five U.S. territories and occurred between February 1 and June 14, 2016.  An extra 716 unpledged delegates (712 votes) or "superdelegates", including party leaders and elected officials, were appointed by the party leadership independently of the primaries' electoral process.  The convention also approved the party's platform and vice-presidential nominee.  The Democratic nominee challenged other presidential candidates in national elections to succeed President Barack Obama at noon on January 20, 2017, following his two terms in office.

Leonard Garment: Leonard Garment (May 11, 1924 – July 13, 2013) was an American attorney, public servant, and arts advocate.  He served U.S. presidents Richard Nixon and Gerald Ford in the White House in various positions from 1969 to 1976, including Counselor to the President, acting Special Counsel to Nixon for the last two years of his presidency, and U.S. Ambassador to the Third Committee at the United Nations.

Libertarian Party presidential primaries, 2016: The 2016 Libertarian Party presidential primaries and caucuses allowed electors to indicate non-binding preferences for the Libertarian Party's presidential candidate.  These differed from the Republican or Democratic presidential primaries and caucuses in that they did not appoint delegates to represent a candidate at the party's convention to select the party's nominee for the United States presidential election.  The party's nominee for the 2016 presidential election was chosen directly by registered delegates at the 2016 Libertarian National Convention, which ran from May 26 to 30, 2016.  The delegates nominated former New Mexico Governor Gary Johnson and former Massachusetts Governor Bill Weld.

Green Party presidential primaries, 2016: The 2016 Green Party presidential primaries were a series of primaries, caucuses and state conventions in which voters elected delegates to represent a candidate for the Green Party's nominee for President of the United States at the 2016 Green National Convention.  The primaries, held in numerous states on various dates from January to July 2016, featured elections publicly funded and held as an alternative ballot, concurrent with the Democratic and Republican primaries, and elections privately funded by the Green Party, held non-concurrently with the major party primaries.  Over 400 delegates to the Green National Convention were elected in these primaries, with a candidate needing a simple majority of these delegates to become the party's nominee for president.

Thomas Graham Jr. (diplomat): Ambassador Thomas Graham Jr. is a former senior U.S. diplomat.  Graham was involved in the negotiation of every single international arms control and non-proliferation agreement from 1970 to 1997.  This includes the Strategic Arms Limitation Talks (SALT Treaties), the Strategic Arms Reduction Treaties (START Treaties), the Anti-ballistic missile (ABM) Treaty, Intermediate-Range Nuclear Forces Treaty (INF) Treaty, Treaty on the Non-Proliferation of Nuclear Weapons Treaty (NPT), Treaty on Conventional Armed Forces in Europe (CFE) Treaty and Comprehensive Nuclear-Test-Ban Treaty (CTBT).  In 1993, Ambassador Graham served as Acting Director of the Arms Control and Disarmament Agency (ACDA) from January to November, 1993 and Acting Deputy Director from November, 1993 to July, 1994.  From 1994 through 1997, he was president Bill Clinton's special representative for Arms Control, Non-Proliferation, and Disarmament.  Graham successfully led the U.S. government efforts to achieve the permanent extension of the NPT in 1995.  Graham also served for 15 years as the general counsel of ACDA.  Throughout his career, Thomas Graham has worked with six U.S. Presidents including Presidents Richard Nixon, Gerald Ford, Jimmy Carter, Ronald Reagan, George H. W. Bush, and Bill Clinton.  Ambassador Graham worked on the negotiation of the Chemical Weapons Convention and the Biological Weapons Convention and managed the Senate approval of the ratification of the Geneva Protocol banning the use of chemical and biological weapons in war, as well as the Biological Weapons Convention.

Reform Party presidential primaries, 1996: Due to the lateness at which the Reform Party had been established, the traditional system of Presidential Primaries that had been in use for some time by the Republican and Democratic parties was not considered practical.  Instead, a national primary would be held through the mail in which Reform Party supporters would be able to vote for a number of candidates, while ballot efforts would be concentrated entirely towards the general election.

Reform Party presidential primaries, 2000: Following Ross Perot's impressive showing during the 1996 presidential election, the Reform Party of the United States of America became the country's largest third party.  The party's 2000 presidential candidate would be entitled to $12.5 million in matching funds.  Several high-profile candidates vied for the nomination, including Donald Trump, Pat Buchanan, and physicist John Hagelin.  For a brief time, Congressman John B. Anderson and Congressman Ron Paul were considered potential candidates, but both ultimately declined to seek the nomination.

Supporting paragraphs: Reform Party presidential primaries, 2000 Pat Buchanan
Answer: Pat Buchanan