@JMS - I don't offer this answer as a substitute, but in addition to yours.
@dwstein - The source for information cited and provided below comes from:
- John Y. Simon, Lincoln and Grant (Lincoln Fellowship of Wisconsin, 1984);
- Brooks D. Simpson, Ulysses S. Grant: Triumph Over Adversity, 1822-1865
(Boston: Houghton Mifflin, 2000);
- Jean Edward Smith, Grant (Simon & Schuster, 2000)
as found summarized on Abraham Lincoln's Classroom.org in the featured article Abraham Lincoln and Ulysses S. Grant. At the bottom of the article there are 138 References cited.
It appears Lincoln's confidence in Grant was solidified with Grant's victory at Vicksburg. Prior to Vicksburg:
General Grant was a source of admiration and source of concern at the White House. Of particular concern was Grant’s reputed fondness for liquor. He began to drink seriously when posted by the army in California. Biographer William S. McFeely wrote
“Without friends, without Julia and the two boys, without any responsibilities on the base, he was at the danger point….Grant did not leave the army because he was a drunk. He drank and left the army because he was profoundly depressed.”
Concern about Grant’s drinking surfaced in late 1861. In Galena, Grant had met his future aide, John A. Rawlins. Rawlins was only person besides Grant’s wife who could protect him from demon whiskey. Historian Kenneth P. Williams wrote:
“On December 30 Rawlins found time to write a very long and important letter. It was an answer to one of the 21st from Congressman Washburne, who was much disturbed by reports that Grant was intemperate. Rawlins said that he had found Grant ‘a strict abstinence man’ when he himself reached Cairo, and he had been told by men who knew Grant well that such had been his habit for the past five or six years.”
Historian James McPherson noted that
“Grant probably drank less than his peers, but he could not hold his liquor well.”
In Late 1861 Grant's drinking was becoming well known in Washington. Rather than relying on rumors, Lincoln and Secretary of War Edwin M. Stanton sent several military and civilian visitors to investigate personally and report their findings back to Washington. Upon their arrival at his headquarters, Grant became aware that his status was cause for concern in Washington. The article goes on to explain:
Among these [visitors] were former New York Tribune editor Charles Dana, Congressman Elihu Washburne, and Adjutant General Lorenzo Thomas – as well as a team of doctors. Rather than taking offence at these visits, Grant received the visitors cordially – realizing that in so doing he could control the substance and tone of their reports. Brooks Simpson wrote: “The positive reports of Dana, Thomas, and the medical officer reassure Lincoln about Grant’s ability.” Lincoln however worried about Grant’s strategy – until he started repulsing and containing the Confederates. Simpson wrote:
“Lincoln believed the campaign ‘one of the most brilliant in the world.’ The six weeks of siege that followed, coming at a time when Robert E. Lee’s army was moving northward into Maryland and Pennsylvania, caused Lincoln some concern, but in the main he was relieved. ‘I rather like the man,’ he told one visitor. ‘I think I’ll try him a little longer.’” [emphasis added]
Shortly thereafter, during the Tennessee campaign:
General Ulysses S. Grant came to the attention of President Lincoln and the nation when in February 1862 Grant captured two Confederate garrisons on the Tennessee River, Fort Henry and Fort Donelson. “U. S.” Grant got the nickname “Unconditional Surrender” Grant after he demanded unconditional surrender from the Confederate commander of Fort Donelson.
While undoubtedly this raised Grant's political capital in Washington, Lincoln still had reservations. But Grant managed to avoid any serious blunders that could have ended his career. The article explains Grant's status with Lincoln prior to Vicksburg like this:
For the first two years of the war, President Lincoln and General Grant had to size each other up from a distance. Historian William B. Hesseltine contended:
“With his work as a military administrator adding nothing to his reputation, Grant’s rise to success was hampered by many difficulties. Contrary to later legend, Lincoln was slow to [perceive] Grant’s fighting qualities.” [emphasis added]
Historian John Y. Simon states:
“While Grant fought the war in the West, his only contact with Lincoln came through correspondence, and there was no great amount of it. Yet the man in the White House kept a careful eye on Grant, who held a series of posts so vital that mismanagement would have been fatal.”
It was Grant's success at Vicksburg that solidified Lincoln's faith in his military abilities, but there were still political questions that remained. According to the article:
What marked Grant for promotion by the President was the surrender and capture on July 4, 1863, of Vicksburg, Mississippi, the last remaining Confederate citadel on the Mississippi River. [emphasis added] If one way didn’t work, Grant tried another to attack the city. President Lincoln had been doubtful about Grant’s strategy, but grateful that it worked. The chief executive followed Grant’s progress on the maps he kept in his office. On July 13, President Lincoln wrote Grant:
“I do not remember that you and I ever met personally. I write this now as a grateful acknowledgement for the almost inestimable service you have done the country. I wish to say a word further. When you first reached the vicinity of Vicksburg, I thought you should do, what you finally did–march the troops across the neck, run the batteries with the transports, and thus go below; and I never had any faith, except a general hope that you knew better than I, that the Yazoo Pass expedition, and the like, could succeed. When you did get below, and took Port-Gibson, Grand Gulf, and vicinity, I thought you should go down the river and join Gen. [Nathaniel] Banks; and when you turned Northward East of the Big Black, I feared it was a mistake. I know wish to make the personal acknowledgement that you were right, and I was wrong.”
As historian James M. McPherson tersely observed: “Grant was…Lincoln’s man the rest of the war.” [emphasis added]
When Grant aide and army chaplain John Eaton visited the White House in 1863,
“Mr. Lincoln immediately began to ask me questions about his ‘fighting General,’ as he already called Grant, passing from him to the consideration of other men whom he trusted, – to the personal characters of various subordinate officers, and what they did and said. The searching inquiries never for a moment became trivial; the motive behind each was too formidable for that. During the whole of my acquaintance with the President, he seemed to me to be doing all in his power to measure the personal character of prominent men. He gauged the strength of his armies by their leaders. He seemed constantly to be taking these measurements, and when he had taken them, to lay them aside in that wonderful brain of his for future use.”
Historian E. B. Long wrote “that all through 1863 Grant shows up more and more as a great organizer of war, a side of his genius too often submerged because of the more spectacular events he engineered.” Long argued that “Lincoln recognized this ability when he ordered Grant east to take command of all the armies and to direct the total war strategy. Lincoln needed a general who could fight, but, even more, one who could coordinate.”
Lincoln wanted a military commander who could direct the entire Union military effort – but not be tempted like Generals George B. McClellan and John C. Fremont – into trying to direct the nation from the White House. Grant scholar John Y. Simon wrote of Lincoln:
“Before appointing Grant lieutenant general, he wanted assurance that the new rank would not be used as a springboard to the White House. Two close friends of Grant from Galena were interviewed and gave full assurance that Grant’s interests were purely military. Only then did Lincoln proceed with the appointment.” [emphasis added]
This article, and the books used and cited as references therein, appear to provide documentary evidence that Lincoln was not sold on Grant until Vicksburg, but prior to that he did exhibit faith in him by not succumbing to rumors about Grant, but rather investigating the matter for himself through trusted emissaries, and watching Grant's progress for signs of military and personal failure or success.
The 138 sources referenced in the above cited article are too numerous to list here, but can all be found at the bottom of the article's page at AbrahamLincolnsClassroom.org.