I recently took a tour of Grant's Tomb in NYC. The guide, an NPS ranger, remarked that historians hadn't been kind to Grant's presidency, well into this century -- one indicator being that his tomb focuses almost exclusively on his Civil War service and virtually zero on his two terms as president.
The ranger said Grant deserved better, and hopefully our ideas of him would be improved because the next biography of him was being written by Ron Chernow, author of "Alexander Hamilton." My group nodded their heads and agreed that was "good news" for Grant's memory.
But then I thought...why? I would assume most modern historians would take a sympathetic view of Grant, due to his work against racism, for conservation, etc. Everyone has access to Grant's autobiography and the papers published after his death. Why is Chernow's involvement "good"? Because Chernow is a "good" historian? How so? No one would question the good he did in restoring Hamilton among the Founders...but is that to his credit, or Hamilton's? Or Lin-Manuel Miranda's?
I have nothing against Chernow or Grant (or Hamilton). I just wonder what Chernow's new status means for his works, how we view his works, and our placement of history in context. What if his biography declares Grant was a despicable tyrant? Should we believe him because he was right about Hamilton?
For Grant himself, see this post by /u/Gunlord500
For me, the criteria of a "Good" historian, besides of course actually formulating a cohesive and useful argument are:
History should be like science. You don't make the observations fit your theory. You make your theory fit the observations and then try your hardest to disprove your own theory.
I think a clear sign of a bad work of history is a lack of source criticism, citation, and failure to argue against the author's own point of view. This especially end up with a story of a good and/or a bad side, whether its individual, group, or idea. And the good side come off as an infallible good that did no wrong, and the bad come off as the spawn of pure evil that did no right. When the work begin to pass judgement, that's a big warning sign. And it often leads to things like "if x had been in charge", "if x had lived longer", "if y hadn't happened", blah-blah. When the historian writes like he's lamenting how the world turned out and wishing it could have been different, you know he's doing terrible.
Not only is this shady historical work, it's not helpful. If we say everything Hitler did was bad because he was pure evil, what does that teach us? Absolutely nothing.
There is no such thing as objective truth. At least in the eyes of most historians today, E.H. Carr's school of thought.
Both the bad historian and the good historian, as you mentioned, have the same facts before them, or at least available to them. Before them they have Ulysses Grant's diaries, doctrines, speeches etc. etc. etc., yet they decide to implement them differently, to analyse them differently, to interpret them differently.
The 'good' historian coherently and transparently comes to a precise conclusion, the 'bad' historian trembles, is unpersuasive and twists the facts to fit his own view rather than letting them speak for themselves. Don't get me wrong, its not about writing the best fiction but about how to best implement and interpret facts. Very basically put.
Therefor, if the biography would declare that Grant was a despicable tyrant than you should just see it as one individual interpretation but not as the "truth". You should never fully "believe" the interpretation of a historian or think that it is fully "right". Do not judge the interpretation with the reason that in todays society Grant should be perceived as morally right for that would be egoisitic anachronism. Judge it on its integrity and persuasiveness. "There is no such thing as a moral or an immoral book. Books are well written, or badly written".
Read other accounts on Grant don't just take one account from one historian for granted. Having the same access to facts, historians will come to a similar conclusion, but alas their interpretations will still vary due to their own perception, predisposition, preferences. That is the beautiful thing about history. While you learn about Grant's presidency from different interpretations you also learn about the times in which these interpretations were made. For example today we would have a much more positive view of him, "due to his work against racism, for conservation, etc." while the society of the 19th century might have different morals and therefor a partially negative view of him.
Consequently, as you already recognised, our contemporary perception, or at least that of the broad public, of a historic figure is largely influenced by historians or the public portrayal of the specific figure, take Lin-Manuel Miranda or, even better, Shakespeare's Macbeth as an example. This does not mean however that only the one who interprets takes credit, as there is factual prove of e.g. Hamilton's, of what we would call today 'good' and 'bad', personal aspects that validate or disapprove his historical position.
History, like the weather (unless you live in England where it is always raining), constantly changes and thats why different statūs, such as Chernow's, are so exciting. I really like Wilde's quote: "The one duty we owe to history is to re-write it".
I can't comment on Chernow specifically (or Grant for that matter) but what makes a good historian is in many ways bringing new perspectives and interpretations to things that are soundly argued and based upon evidence.
Good historians discover a new and convincing perspective on things that previously wasn't seen or clear. Through the use of good questions and arguments stemming from sources and their interpretation they uncover connections previously unseen that hold explanatory potential.
E.g. why do people – and that includes people that do not agree with him politically – regard Eric Hobsbawm as a good because his four books on the 19th and 20th century were sweeping overviews of modernity based on extensive research and bringing a new and fresh perspective to the material – a serious marxist interpretation of modernity that holds great explanatory potential as to how and why things transpired the way they did.
Another such case is Lynn Hunt e.g. She pioneered the New Cultural History in the 80s, which takes techniques and methods from anthropology and looks at popular culture and traditions and interprets them historical. Her work was focused on popular symbols of the French Revolution and by charting how the tricolore or the Marseillaise came to the symbolic place they hold, how they spread, and what they meant for the people she further our understanding of that revolution immensely.
It's the historians essential mission to further and deepen our understanding of past events. Good historians do that, not just through good source critique but also through bringing new perspectives and new questions to the table that fit into a mosaic picture of the whole and go a long way in giving us insight into how and why things turned out as they did.
This can take many forms. I haven't read Chernow but pointing to a greater importance of a figure that was previously assigned little importance like Alexander Hamilton is exactly this. It helps transform and further our understanding of the founders and their politics. Now, with Grant, questions such as how does he fit in the general direction US history was taking at the time and how did he influence it, how did his presidency shape the America to come and how was it shaped by the events that transpired before etc. would be questions a good historian would attempt to answer based on the material available.