By Will Dunham
WASHINGTON (Reuters) - Tennessee Republican Howard Baker, a pivotal figure in the Senate Watergate inquiry that pushed U.S. President Richard Nixon toward resignation and who later helped salvage Ronald Reagan's presidency amid the Iran-Contra scandal, has died. He was 88.
Baker stood out during the Senate's 1973 Watergate hearings by asking witnesses, "What did the president know and when did he know it?"
Baker's death was announced on Thursday on the Senate floor by Republican Leader Mitch McConnell, who called him "one of the Senate's most towering figures."
Baker, a courtly moderate, served as Reagan's chief of staff from 1987 to 1988 and as President George W. Bush's ambassador to Japan from 2001 to 2005. He ran unsuccessfully for the 1980 Republican presidential nomination.
Baker was elected as a senator from Tennessee in 1966 and served 18 years, including four as Senate majority leader.
A low-key, consummate Washington insider who built a reputation as a power broker and consensus builder, Baker managed to win bipartisan respect and friendship while still being gifted at partisan politics.
"Senator Baker truly earned his nickname - the Great Conciliator," McConnell said. "I know he will be remembered with fondness by members of both political parties."
Baker may be most remembered for the simple question he posed to witnesses appearing before a special Senate committee investigating Watergate - including John Dean, who served as Nixon's White House counsel - aimed at ascertaining the president's knowledge of events surrounding Watergate.
The scandal involved a break-in at the Democratic National Committee headquarters in the Watergate building and the ensuing cover-up of White House involvement.
Baker, who was vice chairman of the Senate Watergate committee led by Democrat Sam Ervin, initially believed that fellow Republican Nixon had done nothing wrong. But as the investigation unfolded, he became convinced of wrongdoing within the administration.
Baker would not even have been a member of the Senate committee had he accepted Nixon's offer a couple of years earlier to serve on the U.S. Supreme Court. But Nixon was reported to have grown impatient waiting for Baker to respond and instead nominated William Rehnquist.
Nixon asserted that he knew nothing about the break-in but Dean testified that Nixon had approved plans to cover up White House involvement.
Alexander Butterfield, another former Nixon aide, also testified that Nixon had operated a voice-activated tape recorder system in the White House.
Nixon refused to hand over the tapes and the committee - at Baker's urging - sued the president unsuccessfully for access to them. The Supreme Court later ruled in a separate case that Nixon had to turn over the tapes to a special prosecutor.
In 1974 Nixon became the first U.S. president to resign.
Baker rose to the top of the Senate's leadership during his 18 years there. He was the Senate minority leader during Democrat Jimmy Carter's presidency from 1977 to 1981.
After Republicans took control of the Senate with Reagan's victory over Carter in 1980, Baker became the majority leader from 1981 until 1985, when he retired from the Senate. Baker viewed himself as Reagan's lieutenant in Congress during his first term as president, helping shepherd his agenda.
Reagan soon turned to Baker again. In 1987, Reagan was mired in a scandal involving arms sales to Iran in exchange for U.S. hostages in Lebanon, with proceeds diverted to fund anti-communist rebels in Nicaragua in violation of U.S. law.
The Tower Commission, a presidential panel that investigated the scandal, blistered Reagan's advisers for giving him poor advice and exposing the administration to legal and political risks. Reagan then fired Donald Regan as White House chief of staff and asked Baker to replace him.
"I think the president was damaged by some allegations of the Tower Commission but it's more important that he survived, and I think he's going to grow from this point in strength and popularity," Baker said upon taking the job.
Baker won high marks for a shrewd, calming performance as Reagan's right-hand man. But Baker, who came up short against Reagan in the race for the 1980 Republican presidential nomination, gave up plans to run again in 1988 to take the job.
During his time in the Senate, Baker built a record as a moderate who sometimes differed with others in his party, as with his support of the 1977 treaty championed by Carter that returned control of the Panama Canal to Panama.
He earned respect among lawmakers of both parties.
"Make no mistake, he was a tough competitor but he always remained amiable and friendly to work with, in short, a gentleman in the true sense of the word," Democrat Robert Byrd, the longest-serving senator ever, said of Baker during a 2005 tribute. "He was necessarily partisan but not overly so."
Howard Henry Baker Jr. was born on Nov. 15, 1925, to a family of politicians and lawyers in the Cumberland Mountains town of Huntsville. His grandmother was Tennessee's first female sheriff and his father and stepmother both served in the U.S. House of Representatives.
In 1950, he married Joy Dirksen, daughter of Illinois Senator Everett Dirksen, and the couple had two children. Joy Baker died in 1993.
In 1996, he married Senator Nancy Kassebaum of Kansas, whose father, Alf Landon, was governor of Kansas and the Republican presidential candidate who lost to President Franklin Roosevelt in 1936.
(Writing by Will Dunham; Editing by Bill Trott and Susan Heavey)