In 1865, Heiskell was again elected to the
Tennessee House of Representatives, this time representing
Knox County. When the House convened on April 3, Heiskell was elected Speaker, defeating James R. Hood of
Hamilton County by a vote of 37 to 29. Among the first orders of business was the ratification of the
Thirteenth Amendment, which easily passed the House and was certified on April 7. The legislature also passed the "franchise law," which barred ex-Confederates from voting. Heiskell voted against the latter, prompting calls for his resignation from the allies of Brownlow, who was now governor. Throughout the summer of 1865, the rift between Brownlow's allies, who had aligned themselves nationally with the
Radical Republicans, and the "Conservative Unionists," who had aligned themselves with President Andrew Johnson, continued to grow. Conservative Unionists, led by Heiskell, were outraged when Brownlow threw out thousands of votes in the August 1865 congressional elections, allowing Radical candidate
Samuel Arnell to win in the
6th district. The Conservatives also endorsed Johnson's veto of the
Freedmen's Bureau bill in early 1866, which Radicals in Congress and Tennessee had championed. The struggle between Radicals and Conservatives touched off an editorial war in newspapers across the state. The
Pulaski Citizen endorsed Heiskell's stance, stating he had used his "best efforts" to maintain harmony and order in the legislature, and the
Cleveland Banner stated that Mullins was "In the Legislature of Tennessee making an ass of himself." Frederick Heiskell, William's brother, published a "scathing" denunciation of Brownlow in the
Knoxville Commercial. Brownlow's
Whig derided Frederick Heiskell as a "superannuated, shallow-brained, malignant, personally corrupt man." In July 1866, Brownlow called a special session of the legislature to consider the
Fourteenth Amendment, which Radicals supported, but Conservatives, including Heiskell, opposed. After the amendment cleared the state senate, its opponents in the state house, lacking the votes to stop its passage, once again fled the Capitol to prevent a quorum. In response, the house sergeant-at-arms rounded up two and confined them to the committee room. Heiskell ruled that this did not constitute a quorum, but the house overrode his decision, and the amendment was passed. Heiskell refused to sign it, and resigned the speakership in disgust. The Speaker
pro tempore, John Norman, signed the amendment, however, and Brownlow quickly certified its ratification. ==Later life, family and legacy==