or governor of texas for that matter.

actually learned to speak passable Spanish!

our nation’s founding fathers wouldn’t have been spinning in their graves for the past 100+ years over the fact that the U.S. A. had become an imperialistic nation. I think the U.S. probably would have eventually become one anyway, because there have long been American business interests wanting Asian markets, and there will probably continue to be - but at least it wouldn't have happened when it did if the Spanish has won the war. In the early 1900s there were American imperialists who wanted to plant the American flag in certain Asian countries to “civilize” the inhabitants as a part of their God-given responsibility as members of the “white race,” God’s “chosen people,” or so they told themselves (much as the British told themselves regarding India). I like knowing that both Silver Democrats as well as Gold Democrats, along with labor leaders, were anti-imperialists, and that Mark Twain and Jack London were too. Same with Mother Jones and Andrew Carnegie.

How would things here be different now? Impossible to say, but much would depend on whether America became an imperialistic power later, regardless of having lost the Spanish American War.

I'm not a big Harry Turtledove fan (or even a critic), but he is the obvious choice to write the novel.

Presumably if the U.S. never had controlled the Philippines, we would have been spared McKinley's rumination that "there was nothing left for us to do but to take them all, and to educate the Filipinos, and uplift and civilize and Christianize them...." And presumably, as you say, the economic motives for some form of imperialism would have remained; how soon and how forcefully the U.S. could act on them would depend in part on how badly it lost the war.

Hmm. I'm inclined to think not much difference in the long run, but I agree that it's impossible to say. To the extent that white man's burden was a driving motive for U.S. imperialism rather than essentially a pretext, losing the Spanish-American War might have gone far to discredit it. (Even winning the Spanish-American War went pretty far to discredit it....)

Internationally
A loss in the Spanish-American War would have left us without possession of either Guam or the Philippines; without Guam or the Philippines, we would have had no way to project power into the Pacific. Thus, there would have been no reason for Japan to attack us at Pearl Harbor.

The consequences of this are considerable. We would have entered the war later, fighting only in the ETO. This probably would have concluded the European war more quickly (because we could throw all our resources at one theater), but would have allowed Japan to empire-build unencumbered. It also would mean that we wouldn't have dropped the atomic bombs.

What would follow would be an uneasy peace with Japan, that would thaw into an alliance of convenience once Mao came to power in China; the oppositional Asian power there to check him would suddenly be our best friend.

Bonus: no Vietnam; that would be Japan's headache.

Domestically
The loss would almost certainly turn the Republicans out of office in 1900, and with the election of Williams Jennings Bryan -- a populist anti-imperialist -- U.S. politics would have taken a decidedly different and more radical turn. Faced with Bryan, it's hard to imagine the Roosevelt-Taft progressive wing of the GOP exercising any dominance (indeed, it's entirely possible that Theodore Roosevelt might not have come to national prominence at all), and thus hard to imagine any significant influence wielded by middle-class progressives (who were by-and-large Republican). Instead, a shamelessly pro big-business GOP might well emerge 20 years ahead of schedule -- but as a minority party -- and US politics might take on a more decidedly European, class-based cast.

Most depressing possibility: without TR, no FDR.

There, that was fun.