While I consider Lincoln one of the greatest purely political minds in American history, his approach to including various people in Cabinet out of political considerations turned out to be an extremely mixed bag when it came to governance. He alienated allies and put unqualified people (ahem, Simon Cameron) into key positions that hampered the early Union cause.
It was honestly kind of a mess and made Lincoln's early years far more difficult than they needed to be. It also didn't really have much of a political pay off, since his re-election hinged on the war effort more than the political alliances he was attempting to finagle ("Atlanta is ours and fairly won." ) Grant and Sherman did more to re-elect Lincoln than any politician or newspaper editor he was trying to woo. (And Stanton plucking around troops to vote. Stanton was ruthless and very effective).
It's a bit of pop history that was simplified down to give a mythologizing portrait of Lincoln. Kearns is a solid historian, but she was kind of writing with a more popular narrative in mind that doesn't serve the material well, IMHO.
I've probably read two dozen books about Lincoln in my life, and ToR is a fun read, but the actual history was far more complicated, gritty, and full of bad decision making. This idea that these rivals came together as a super team under Captain Am- . . . President Lincoln is . . . a very rosy view of what happened.
And it was written as President Obama was coming in. So the optimism of that moment played well with Kearns' portrayal in the media rounds.