The link will give you an idea of what is covered in the book ... often with much more detail of the political nuts and bolts, how the wives impacted their husbands (pretty natural for many women, it goes back to Eve) and most of all, the worship of "progressivism".
The assumption is "progressivism is good" of course. We are "progressing", but towards what exactly? In many ways, we have never moved from the age of the "Bully Pulpit", except the press has become even more biased, and of course we have a lot more technology than was present then.
While the book really never mentions the vast influx of immigrants (legal then), but only the result - exploitation, low wages, slums, crime, unionization, etc. Why did they come and stay? Obviously because the conditions they found here were much better than the conditions they had in Europe, in which opportunity was very limited, and in some cases (Irish) so bad that starvation was an issue.
As is always the case when there is a massive influx of poor, there was exploitation by business and moderately wealthy, through low wages, poor living conditions, and the exploitation of their vulnerability by political machines.
Today, we have massive illegal immigration, and the results are the same -- low wages, poor living conditions, and limited opportunity (they are illegal after all). However, business and the moderately wealthy (remember "Nannygate" in the Clinton years). Why do they come? Because as bad as we see conditions for them here, they are way better than where they come from.
Today, press bias is even more celebrated than it was then. However at the turn of the centruy, the bias was declared, as it is often denied today. Income disparity today is greater than it was then, and the Davos elite, Google, Amazon, WalMart and the massive Deep State keep the "deplorables" in relatively hopeless conditions -- albeit with more entertainment in their increasingly isolated masked homes. Back then at least they mostly had church, family, and ethnic unity/traditions. Today, isolation and increasing government dependence make their lives more meaningless, often with the result being lonely addiction and suicide.
On page 445, Teddy is quoted as saying "...to see the nation divided into two parties, one containing the bulk of the property owners and conservative people, the other the bulk of the wageworkers and the less prosperous people generally; each party insisting upon demanding much that was wrong, and each party sullen and angered by real and fancied grievances".
We have "progressed" so far in 100 years!
In 1906, power and fame had not fully corrupted Teddy and he still had some grasp of reality:
"I must represent not the excited opinion of the West but the real interests of the whole people". Those interests would be ill served he curtly rejoined by turning the operation of the railroads over to government employees for "he knew better than anyone else could how inefficient and undependable they were".
One might think that Amtrak would have finally proven that point, but in 100 years, half the country still thinks more government, and even socialism is a "bully idea".
I much enjoyed learning a lot more about Taft. The saddest part of the book is how Teddy's lust for power and narcissism destroyed their friendship, although somewhat like Jefferson and Adams, they did reconcile before death.
As always, unforeseen events affect history. On April 10, 1912, Major Archie Butt, a friend and go-between between Teddy and Taft was killed when the Titanic sank. He was a great support to Taft, and his loss during the incredibly rancorous election of 1912 added to Taft's pain.
There are good many parallels between Teddy and Trump -- both upper class, willful, often nasty, extremely popular with the "masses", and quite shallow and unrealistic about what they could accomplish against "the system".
Kearns Goodwin is a leftist "progressive" ideologue and the book is absolutely written from that perspective. What is left out (massive immigration at the time being a major example), and near total blindness to the downsides of mob rule, need to be considered if one chooses to dive in. It is overly long for what it covers, but decently written, and gives a good one sided view of the turbulent turn of the 19th to 20th century time.