Allan Burton Spetter, "Frelinghuysen, Frederick Theodore," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00398.html.
Along with many of his contemporaries, [Frelinghuysen] quit the Whig party, as it disintegrated in the early 1850s, and eventually moved into the new Republican party. Frelinghuysen did not participate as a "founding father" of the new party, however, because he agonized for several years over his decision to abandon the Whigs. His family felt a unique attachment to the party, which had offered the nation the ticket of Henry Clay for president and Theodore Frelinghuysen for vice president in the election of 1844. By 1860, however, Frederick Frelinghuysen enthusiastically supported the Republicans and endorsed Abraham Lincoln in his bid for the presidential nomination.