He's a freaking SOCIALIST for Pete's sake!
Here, just look at what he said in his public campaign speeches:
"Equality of opportunity means that the commonwealth will get from every citizen the highest service of which he is capable. ... When I say I want a square deal for the poor man, I do not mean that I want a square deal for the man who remains poor because he has not got the energy to work for himself. ... Now, this means that our government, National and State, must be freed from the sinister influence or control of special interests. .... We must drive the special interests out of politics... For every special interest is entitled to justice, but not one is entitled to a vote in Congress, to a voice on the bench, or to representation in any public office. ... The citizens of the United States must effectively control the mighty commercial forces which they have themselves called into being."
"Of course there are many sincere men who now believe in unrestricted individualism in business, just as there were formerly many sincere men who believed in slavery -- that is, in the unrestricted right of an individual to own another individual. ... The effective fight against adequate government control and supervision of individual, and especially of corporate, wealth engaged in interstate business is chiefly done under cover; and especially under cover of an appeal to States' rights.... The proposal to make the National Government supreme over, and therefore to give it complete control over, the ... instruments of interstate commerce is merely a proposal to carry out to the letter one of the prime purposes, if not the prime purpose, for which the Constitution was founded. ... The truth is that we who believe in this movement of asserting and exercising a genuine control, in the public interest, over these great corporations have to contend against two sets of enemies, who, though nominally opposed to one another, are really allies in preventing a proper solution of the problem. There are, first, the big corporation men, and the extreme individualists among business men, who genuinely believe in utterly unregulated business -- that is, in the reign of plutocracy; and, second, the men who, being blind to the economic movements of the day, believe in a movement of repression rather than of regulation of corporations."
And still again:
"I believe that the natural resources must be used for the benefit of all our people, and not monopolized for the benefit of the few, and here again is another case in which I am accused of taking a revolutionary attitude. People forget now that one hundred years ago there were public men of good character who advocated the nation selling its public lands in great quantities, so that the nation could get the most money out of it, and giving it to the men who could cultivate it for their own uses. We took the proper democratic ground that the land should be granted in small sections to the men who were actually to till it and live on it. Now, with the water-power, with the forests, with the mines, we are brought face to face with the fact that there are many people who will go with us in conserving the resources only if they are to be allowed to exploit them for their benefit. That is the one of the fundamental reasons why the special interests should be driven out of politics.... Let me add that the health and vitality of our people are at least as well worth conserving as their forests, waters, lands, and minerals, and in this great work the national government must bear most important part."
Need more evidence? Look at what he wrote in his own autobiography:
As regards what I have said in this chapter concerning Socialism, I wish to call especial attention to the admirable book on “Marxism versus Socialism,” which has just been published by Vladimir D. Simkhovitch. ... Every social reformer who desires to face facts should study it—just as social reformers should study John Graham Brooks’s “American Syndicalism.” From Professor Simkhovitch’s book we Americans should learn: First, to discard crude thinking; second, to realize that the orthodox or so-called scientific or purely economic or materialistic socialism of the type preached by Marx is an exploded theory; and, third, that many of the men who call themselves Socialists to-day are in reality merely radical social reformers, with whom on many points good citizens can and ought to work in hearty general agreement, and whom in many practical matters of government good citizens well afford to follow.
As if that were not clear enough, he devoted his political career to curbing the power of large corporations, to supporting the right of workers to unionize, to passing strict and unprecedented regulations on the pharmaceutical and banking industries, and to creating entirely new federal governmental agencies for the protection of the environment (he even supported huge government land grabs to turn private acreage into public lands)!
We're still talking about Republican President Teddy Roosevelt, right?