Complex sentence: Were Taft and Roosevelt voters united behind a single Republican candidate, they would have taken a combined majority of over 61 percent of the vote, but the split would instead prove fatal to the Republicans both nationally and in Massachusetts.
Split into simpler sentences: Were Taft and Roosevelt voters united behind a single Republican candidate, they would have taken a combined majority of over 61% of the vote. But the split would instead prove fatal to the Republicans both nationally and in Massachusetts.