Indeed...apparently, he volunteered for combat IOTL, but he never saw combat, a pity...
Now, had he been President on March 4th of 1897, how long till a war of liberation? would he have still waited until 1898? or maybe even longer?
Any important effect without TR as Assistant Secretary of the Navy?
Can the war assure reelection for Bryan in 1900?
The Spanish-American War was not inevitable by any means. The explosion that destroyed the Maine has been shown to have been caused by a flaw in the way the engine room and the gunpowder stores were placed in the ship. So its entirely possible that the butterflies from Bryan's election mean the Maine explodes in the middle of the ocean or in an American port.
Furthermore, although the United States was being wiped into a frenzy over the Spanish atrocities, there had been campaigns like that before that didn't result in the United States launching a war of foreign conquest.
At this time there was a difference in the Union Movement over whether to create a Political Movement and work for rights and Improvements for all workers, or to concentrate the Union Movement on Immediate benifits, and Improvements of specific workers.
OTL Samuel Compers, and his "Immediate "strategy won.
I wonder if TTL, may not see the country polarized enuff to tip the Balance in Favor of a American Labor Party.
I don't know about a separate American Labor Party, but I think that a Labor Movement that is highly politicized and allied to the Democratic Party is a highly likely outcome of Bryan's victory.
If you have a more politicized movement, I think Eugene Debs would be one of the men who would be in the forefront of that movement. His views on industrial unions and willingness to use direct action, combined with an electoral alliance with Bryan's Democratic Party, could change the path of the both organized labor and the Democratic Party. Debs had been elected to office as a Democrat prior to his involvement in the American Railway Union and his imprisonment for leading the Pullman Strike. Given a markedly more pro-labor political climate Debs might stay in labor organizing, and take advantage of the political space provided by Bryan to make gains.
The rise of organized labor, combined with the pro-business Bourbon Democrats walking away from the Democratic Party in the '96 election (and running a separate ticket), rises the possibility that Bryan's victory will create FDR's 'New Deal' coalition a generation early, with political labor, the northern city bosses, and populist-tinged southerners.
As it turned out Teddy Roosevelt made the difference and brought in anti trust measures in a way that worked. Bryan would have been divisive (religious bigotry) and engender strong opposition and there is no guarantee that his economic policies would have worked.
The country was in a protracted economic depression at the time of the 1896 election. Bryan's embrace of the Populists' main plank, bimetalism, brought him the '96 Democratic nomination (the speech that got him the nomination was called "Cross of Gold"- you get the idea). While some of his economic platform might not have been doable, his opposition to monopolitisic corporations is going to have big, immediate effects. Roosevelt's anti-trust action was not a really serious attempt to address the problem of monopolitistic corporate practices, it was merely a (successful) attempt to defuse some of the anti-corporate anger that can be seen in Bryan's electoral coalition and the events that were occuring at the time. Bryan would be challenging not only the monopolitistic practices, but he would be holding out the possiblity that the federal government would simply nationalize certain industries. That kind of a stick would probably get major concessions out of the trusts, concessions that Roosevelt's basically pro-business stance never did.
Trust-breaking and supporting organizing labor. Bryan would be striking at the heart of the American status quo circa the turn of the 20th century. If he does get killed in 1900, his bloody shirt might provide the electoral firepower to push his reforms over the top.
If Bryan can make headway in fighting monopolies, I think he'll have a good chance of winning re-election in 1900. That he won and the world didn't end the day after (many factory owners told workers that the factory would shut down if Bryan won the election) and in fact made some major gains for the working classes, is going to give him a big rhetorical leg to stand on. In 1900 he'll be running against the trusts, not the GOP.