Complex sentence: In 1912, Clark was the frontrunner for the Democratic presidential nomination, coming into the convention with a majority of delegates pledged to him, but he failed to receive the necessary two-thirds of the vote on the first several ballots.
Split into simpler sentences: In 1912, Clark was the frontrunner for the Democratic presidential nomination, coming into the convention with a majority of delegates pledged to him. But he failed to receive the necessary two-thirds of the vote on the first several ballots.