1912 the most consequential election in world history

[zorkpolitics]

In 1912 The Republicans failed to nominate Roosevelt and opened the path for Wilson when Roosevelt and Taft split the Republican coalition.

How would another Roosevelt term have changed history?

Internationally Roosevelt was the most respected world leader, already he had won a Nobel Peace Prize for ending the Russo-Japanese war in 1905.  If Roosevelt had been President in 1914 he would have almost surely of intervened at the start of WWI.  By force of will he would have brokered a compromise and prevented a war that neither England nor Germany wanted (remember the ruling families were cousins).
Without the Russian-German conflict in WWI, the Czars retain power and the Bolsheviks never come to power: no Lenin, no Stalin, no 30 million soviets killed from purges and famines. 
Without WWI, Europe continues their evolution towards parliamentary rule, 9 million are not killed in WWI.
Without Versailles, no rise of German Nationalism, no Hitler, no 6 million Jews killed.
No Hitler in power, no WWII in Europe, 50 million people are not killed.
The Japanese still wage war, there is still Pearl harbor, but the US and the British Empire defeat Japan sooner.
Atomic Bombs are not developed until the 1960's, none are used against Japan.
Israel does not become Zionist state, and the Middle East does not become the fulcrum of western-Islamist conflict.  Palestinian terrorism, Al Qaeda, and Islamist terrorism does not become a major problem, no 9/11.
Technology and cultural changes unfolds more slowly:  no cold war to push innovation, Jet travel is delayed for decades, we never go to the moon, the first person in space occurs in the 1980's not 1960's.  Without integration in the military during WWII, civil rights are delayed and much more limited.   GDP growth is half what it has been since WWII.
European colonialism lasts longer and the third world doe snot become a surrogate conflict between the Soviets and the West.
As the century ends personal computers are just beginning to appear, but there is no Internet, no green revolution, famines have killed millions in Africa, Asia and South America.

[zorkpolitics]

Without the Russian-German conflict in WWI, the Czars retain power and the Bolsheviks never come to power: no Lenin, no Stalin, no 30 million soviets killed from purges and famines. 

I'm not convinced by your reasoning. I doubt Tsarist rule would last very long. Rather, you'd have a model of February Revolution succeeding, maybe later.

Of course we'll never know, but the Tsarist rule was really pushed over the edge by the war, of course given the craziness of the royal family, they very well may not have lasted much longer.  But I don't see Lenin being inevitable...