Because both Reagan and Bush saw him as a potential threat. Kissinger was probably the most independent Secretary of State in American history during the Ford administration. His fame and credibility as a foreign policy expert endured after leaving the White House: according to biographer Thomas Schwartz, "A LexisNexis survey from 1975 through 1987 showed 10,187 mentions of Kissinger in the press, behind only President Reagan and Elizabeth Taylor". Because of this, he was indispensable on the campaign trail and as a tool to "sell" administration foreign policy, but, if he were invited back into the White House, could quickly prove a rival to the President. Reagan and Bush were afraid of such a "co-presidency", and kept Kissinger at arms' length. Both made one of Kissinger's close associates Secretary of State, but refused to nominate the man himself to the cabinet.

Henry Kissinger's first bid to return to power was during the 1980 campaign. Ostensibly, his chances looked good, as no candidate minus George H.W. Bush ruled out his nomination as Secretary of State. Kissinger was given a "primetime" speech at the Republican National Convention, where he launched an unusually partisan attack on Jimmy Carter's foreign policy, but, since this speech took place at midnight after a night of long speeches whose time was not moderated, the audience was largely asleep. Nevertheless, Kissinger proved a vital campaign asset for Reagan: he helped to sway the Jewish vote, and re-assured the press that Ronald Reagan was mentally fit to conduct foreign policy. Kissinger was appointed to Regan's transition team, and used this access to lobby for the appointment of Gerald Ford as Vice President.

The Reagan-Ford scheme looked promising at first, but fell through largely over Kissinger. Ford insisted on Kissinger being Secretary of State, which Reagan shot down, stating "I’ve been all over this country the last several years, and Kissinger carries a lot of baggage. I couldn’t accept that. My own people, in fact, wouldn’t accept it". What he was referring to was Kissinger's callous pragmatism, which had turned off many on the "New Right", a rising idealistic faction of the Republican party which sought to evangelize the world more than it sought to deal with it. In the words of one Reagan aide, “If Henry Kissinger was put back into the State Department, Jesse Helms [a chief leader of the New Right] would commit hara-kiri on the White House lawn.”

Kissinger backed away from his demand to be Secretary of State, but Ford was insistent on having power over the National Security Council and "real responsibilities" as Vice President. By this stage in negotiations, "Reagan’s people certainly believed Kissinger was attempting a 'power grab,' and they told Howell Raines of The New York Times, 'Kissinger simply saw a Ford Vice Presidency as his ticket back to power.'"

Kissinger and his associates were essentially locked out of the Reagan administration for two years, but Kissinger worked his way back in through publicly supporting Reagan while criticizing those actions of his subordinates that he calculated Reagan also disagreed with. The 1982 dispute between the US and its European allies over dissent in Poland was key to Kissinger's re-entry into the White House. Reagan's circle advised caution, deferring to the European position, while Kissinger criticized this as weakness. In 1982, two developments rebuilt Kissinger's influence in Washington: first, his friend George Shultz was appointed Secretary of State, and second, he was made head of Reagan's Central America commission. He was aware that his responsibility would be to "sell" the Reagan foreign policy and not shape it, but nevertheless re-acquired a high profile role. By 1984, however, Kissinger had left the administration and never returned.

Kissinger's short tenure in the Reagan white house was due both to the little power afforded to him by his role, and the reason he accepted it in the first place. Kissinger was by no means idle when he was in the wilderness: opening Kissinger Associates Inc., an international consulting firm, Kissinger made many tens of millions of dollars as a private sector consultant and diplomat. He was essentially "forced" back into the White House by Seymour Hirsch's vituperative biopic The Price of Power, which, among other things, claimed that Kissinger offered to betray secrets about Nixon to George Humphrey in exchange for a diplomatic post when Humphrey seemed poised to win. The Central American Commission was one of the ways Kissinger drowned press coverage of Hirsch's book.

Kissinger again tried to return to power during the Bush years. This was handicapped by the fact that Bush himself was quite an expert on foreign policy, and by the personal animosity between the two. Kissinger once called Bush a "very weak man" in private and was the only person attacked by name in Bush's campaign biography. The former Secretary of State doubled down to repair relations when Bush's candidacy became inevitable, going as far as to praise Dan Quayle, Bush's notoriously dim-witted Vice Presidential pick, as “one of the best informed senators on National Security affairs that I know”. To his credit, Bush rewarded Kissinger's aid in spite of their past animosity. Kissinger Associates Inc. consultants Brent Scowcroft and Lawrence Eagleburger were named National Security Adviser and Deputy Secretary of State respectively.

It appeared as if Kissinger's return to the cabinet would be close by, but hopes of this were shattered by the "Yalta II" affair. After his private associates gained two of the three major foreign policy roles in the Bush administration, Kissinger proposed to Bush that he negotiate with Gorbachev over a permanent settlement to the European question. Having perceived the USSR to be a declining power since the early 1980s, Kissinger argued that Soviet retreat was inevitable, and offered to shuttle between Bush and Gorbachev to procure this settlement. Similar to his "informal" diplomacy with China as National Security Adviser, this attention-grabbing usurpation of the Secretary of State's powers was meant to be a springboard to the Secretary of State job itself. Bush approved the mission, and Kissinger met with Gorbachev the following month.

The agreement that he reached with the Soviet leader involved the "Finlandization" of Eastern Europe, whereby Gorbachev would not use force to suppress political change in his satellite states, and the US would not provide aid to anti-Soviet leaders. Though this was hoped for in many corners in the 1980s, it was rejected by Secretary of State Baker and many in the right wing of the Republican party. Perceiving the USSR to be in decline already, they thought there was no need to "buy what history will give us for free". In the press, this pragmatic arrangement was condemned as "Yalta II".

It is possible that Bush never intended for Kissinger to have a real role in the administration, and sabotaged the Yalta II mission from the start. Before Kissinger even returned from Moscow with Gorbachev's reply, Bush called Gorbachev and thanked him for "being very generous with his time with Henry Kissinger". He assured Gorbachev “They would not necessarily believe everything [Kissinger said] because this was, after all, Henry Kissinger, but they knew the General Secretary had been generous with his time, and they would listen attentively to what Dr. Kissinger said.” Kissinger found out about this incident shortly after arriving, and relations between him and the President remained "chilly" thereafter.

Underlining all of this was a shift in the attitudes of Republican policymakers between the Ford and Nixon years. Precociously, Henry Kissinger declared in 1987 that “As American resources are shrinking, the drive toward global intervention seems to be increasing". While a child could notice that the drive towards global intervention had been increasing at that point, only those with a pulse on economic trends realized that American resources were shrinking. Between the start and end of the Cold War, the US's share of global GDP had actually declined due to the rise of Germany, Japan, China, and South Korea. The far faster decline of the Soviet Union, however, convinced a great number of figures on the "New Right" that the United States was becoming ever more powerful, and that it should seek to impose its ideological framework everywhere. Kissinger embodied the realpolitik of a past era, unsuited to a foreign policy establishment which increasingly made foreign policy decisions based on the ideological values of a country instead of its strategic relevance.

Most of this is drawn from Thomas Schwartz's Henry Kissinger and American Power, published in August of this year.