Where was the fundamental failure in the Provisional Government that enabled the Bolsheviks to eventually seize power in Russia?
I think that there were two fundamental underpinnings that doomed the Provisional Government from being seen as "the answer" to the challenges Russia faced. The first was that its position on World War I was just not embraced by the Russian people. The people of Russia never bought into the war when the Tsar was deposed. The Provisional Government tried to launch another offensive in the war, something that lacked the authenticity and the legitimacy of the people. This lessened the authority of the Provisional Government, contributing to one failure that enabled the Bolsheviks to gain power with greater ease. I think that the genuine sense of being overwhelmed by the task of governance was also another element in the Provisional Government's failure. Once the Provisional Government gained power, it seemed overwhelmed by the task of governing the nation and guiding the nation once they obtained power. The idea of being so weak from a practical point of view made the Provisional Government one that could not govern from a practical point of view. It is the combination of both elements that enabled them to be subverted by the Bolsheviks and, eventually, lose power to them.