Complex sentence: It was not customary in 1848 for a candidate for high office to appear to seek it, and Fillmore did no campaigning, remaining at his comptroller's office in Albany; thus the campaign was conducted in the newspapers and with speeches made by surrogates at rallies.
Split into simpler sentences: It was not customary in 1848 for a candidate for high office to appear to seek it, and Fillmore did no campaigning, remaining at his comptroller's office in Albany. Thus the campaign was conducted in the newspapers and with speeches made by surrogates at rallies.