Question: How many Senators were willing to vote for acquittal?
About the article "Watergate scandal", section "Resignation".

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Thirty-six "guilty" votes were required to remove Johnson from office.
On all three occasions, 35 Senators voted "guilty" and 19 "non-guilty".
As the Constitution requires a two-thirds majority for conviction in impeachment trials, Johnson was acquitted.
Seven Republican senators were concerned that the proceedings had been manipulated to give a one-sided presentation of the evidence.
Senators William Pitt Fessenden (Maine), Joseph S. Fowler (Tennessee), James W. Grimes (Iowa), John B. Henderson (Missouri), Lyman Trumbull (Illinois), Peter G. Van Winkle (West Virginia), and Edmund G. Ross (Kansas), who provided the decisive vote, defied their party by voting against conviction.
After the trial, Ben Butler conducted hearings on the widespread reports that Republican senators had been bribed to vote for Johnson's acquittal.
In Butler's hearings, and in subsequent inquiries, there was increasing evidence that some acquittal votes were acquired by promises of patronage jobs and cash cards. 
Grimes was elected as a Republican to the U.S. Senate in 1859 and reelected in 1865.
He served in the Senate from March 4, 1859, until December 6, 1869, when he resigned due to ill health.
In the Senate, he served as chairman of the Committee on the District of Columbia (in the 37th and 38th Congresses), and the Committee on Naval Affairs (in the 39th through 41st Congresses).
He also served on the Joint Committee on Reconstruction which drafted the Fourteenth Amendment to the United States Constitution.
In 1861 Grimes was a member of the peace convention held in Washington, D.C., in an effort to devise means to prevent the impending Civil War.
In December of 1861, he introduced the senate bill which led to the creation of the Medal of Honor (initially only for Navy and Marine personnel).
During President Andrew Johnson's impeachment trial, Grimes broke party ranks, along with six other Republican senators and voted for acquittal.
These seven Republican senators were disturbed by how the proceedings had been manipulated in order to give a one-sided presentation of the evidence.
Senators William Pitt Fessenden, Joseph S. Fowler, James W. Grimes, John B. Henderson, Lyman Trumbull, Peter G. Van Winkle, and Edmund G. Ross of Kansas, who provided the decisive vote, defied their party and public opinion and voted against impeachment.
After the trial, Ben Butler conducted hearings on the widespread reports that Republican senators had been bribed to vote for Johnson's acquittal.
In Butler's hearings, and in subsequent inquiries, there was increasing evidence that some acquittal votes were acquired by promises of patronage jobs and cash cards.
Grimes died in Burlington on February 7, 1872, aged 55.
He is buried in the Aspen Grove cemetery, in Burlington.
The plot of land that his home was once located on is now home to an elementary school that bears his name.
The town of Grimes, IA is named for James W. Grimes. 
The release of the "smoking gun" tape destroyed Nixon politically.
The 10 congressmen who voted against all three articles of impeachment in the House Judiciary Committee announced they would all support impeachment when the vote was taken in the full House.
On the night of August 7, 1974, Senators Barry Goldwater and Hugh Scott and Congressman John Jacob Rhodes met with Nixon in the Oval Office and told him that his support in Congress had all but disappeared.
Rhodes told Nixon that he would face certain impeachment when the articles came up for vote in the full House.
Goldwater and Scott told the president that there were not only enough votes in the Senate to convict him, but that no more than 15 Senators were willing to vote for acquittal.
Realizing that he had no chance of staying in office, Nixon decided to resign.
In a nationally televised address from the Oval Office on the evening of August 8, 1974, the president said, in part:The morning that his resignation was to take effect, the President, with Mrs. Nixon and their family, said farewell to the White House staff in the East Room.
A helicopter carried them from the White House to Andrews Air Force base in Maryland.
Nixon later wrote that he thought, "As the helicopter moved on to Andrews, I found myself thinking not of the past, but of the future.
What could I do now?…" At Andrews, he and his family boarded Air Force One to El Toro Marine Corps Air Station in California, and then were transported to his home in San Clemente.
Joseph Smith Fowler (August 31, 1820April 1, 1902) was a United States Senator from Tennessee from 1866 to 1871.
Fowler was born in Steubenville, Ohio.
He graduated from Grove Academy in that city and subsequently from Franklin College in New Athens, Ohio in 1843.
He taught school in Shelby County, Kentucky in 1844.
He served as a professor of mathematics at Franklin College in Davidson County, Tennessee from 1845 to 1849.
He studied law in Bowling Green, Kentucky and was subsequently admitted to the bar and practiced in Tennessee until 1861.
He also served as president of Howard Female College in Gallatin, Tennessee from 1856 to 1861.
Fowler was an ardent Unionist.
He served as State Comptroller of Tennessee from 1862 until 1865.
The official "Tennessee Blue Book" states that the holder of that office during this period was "Joseph S. Foster".
It is likely that the "Biographical Directory" is the correct source; the Confederate state government of Tennessee was never very effective and largely dysfunctional due to the early loss of much Tennessee territory to Union forces by the Confederates and also because neither the Confederacy nor slavery had ever had much public support in East Tennessee.
Most of the state was under the control of the Union military government of Abraham Lincoln's appointed governor, Andrew Johnson, for most of the duration of the American Civil War; his government was fairly functional and it is likely that Fowler served this regime as Comptroller and that the "Blue Book" records his name erroneously.
In 1866 Tennessee became the first former Confederate state to be readmitted to the Union; the Tennessee General Assembly elected Fowler to the Senate, where his service began on July 24, 1866.
Fowler became a part of the majority Republican caucus.
In the 40th Congress he served as chairman of the Committee on Engrossed Bills.
During President Andrew Johnson's impeachment trial, Fowler broke party ranks, along with six other Republican senators, and in a courageous act of political suicide, voted for acquittal.
These seven Republican senators were disturbed by how the proceedings had been manipulated in order to give a one-sided presentation of the evidence.
Senators William Pitt Fessenden, Joseph S. Fowler, James W. Grimes, John B. Henderson, Lyman Trumbull, Peter G. Van Winkle, and Edmund G. Ross of Kansas, who provided the decisive vote, defied their party and public opinion and voted against impeachment.
After the trial, Ben Butler conducted hearings on the widespread reports that Republican senators had been bribed to vote for Johnson's acquittal.
In Butler's hearings, and in subsequent inquiries, there was increasing evidence that some acquittal votes were acquired by promises of patronage jobs and cash cards.
He did not seek a subsequent term in the Senate upon the expiry of his term in 1871.
He also did not return to Tennessee to live, but remained in Washington DC, practicing law there until shortly before his death in 1902.
His remains were interred at Lexington Cemetery in Kentucky. 
As a United States Senator representing a slave state, Henderson co-authored and co-sponsored the Thirteenth Amendment to the United States Constitution permanently prohibiting slavery in the United States.
Henderson's original proposal, made January 11, 1864 was submitted to the Senate Judiciary Committee, and on February 10, 1864 it presented the Senate with a proposal combining the drafts of congressmen James Mitchell Ashley (Republican, Ohio), James Falconer Wilson, (Republican, Iowa), Charles Sumner (Republican, Massachusetts), and Henderson.
On January 31, 1865 the 13th Amendment was approved by the U.S. Congress, and on February 1, 1865 it was signed by President Abraham Lincoln.
On April 14-15, 1865 Lincoln was assassinated before the amendment was ratified by the State of Georgia on December 6, 1865.
While in the Senate, Henderson was chairman of the Committee to Audit and Control the Contingent Expense (Thirty-ninth Congress) and a member of the Committee on Indian Affairs (Thirty-ninth and Fortieth Congresses).
During President Andrew Johnson's impeachment trial, Henderson broke party ranks, along with six other Republican senators and voted for acquittal.
These seven Republican senators were disturbed by how the proceedings had been manipulated in order to give a one-sided presentation of the evidence.
Senators William Pitt Fessenden, Joseph S. Fowler, James W. Grimes, John B. Henderson, Lyman Trumbull, Peter G. Van Winkle, and Edmund G. Ross of Kansas, who provided the decisive vote, defied their party and public opinion and voted against impeachment.
After the trial, Ben Butler conducted hearings on the widespread reports that Republican senators had been bribed to vote for Johnson's acquittal.
In Butler's hearings, and in subsequent inquiries, there was increasing evidence that some acquittal votes were acquired by promises of patronage jobs and cash cards.
Henderson was not a candidate for reelection to the Senate in 1868 and left the U.S. Senate on March 4, 1869.
Henderson was an unsuccessful candidate for Governor of Missouri and later U.S.
Senator.
In 1875 he was special United States attorney for prosecution of the Whiskey Ring at St. Louis.
In 1877 he was appointed a commissioner to treat with hostile tribes of Indians.