Complex sentence: He won his seat even as the Republican presidential candidates in 1920 and 1924, Warren G. Harding and Calvin Coolidge, were losing the electoral vote of Texas, which had supported Democrats for president since the end of Reconstruction.
Split into simpler sentences: He won his seat even as the Republican presidential candidates in 1920 and 1924, Warren G. Harding and Calvin Coolidge, lost the electoral vote of Texas. The Democratic-majority state had supported Democrats for president since the end of Reconstruction.