In a letter announcing her resignation as Buchanan's presidential campaign co-chair, Fulani said Buchanan put his conservative issues above their common interests in political reform, trade and foreign policy.
"I must and do object to your efforts to transform the party into a party of, and for, only social conservatives," Fulani wrote Buchanan.
She said Buchanan's political maneuverings to consolidate power were "contributing to polarizing, rather than unifying the disparate forces in the party."
Fulani's endorsement of Buchanan surprised many. Fulani, a far-left advocate of Marxist-Leninist politics, and Buchanan are on the opposite end of the political spectrum on almost every issue.
Bay Buchanan, her brother's campaign manager, said she enjoyed working with Fulani and regrets her departure. She rejected Fulani's criticisms.
"We have not indicated that we do not welcome people with different views," Bay Buchanan said. "But clearly Pat is not going to walk away from those issues."
Fulani, who will remain in the Reform Party, also complained that Buchanan and his sister refused to support her bid to become the national chairwoman of the party founded by Ross Perot.
"Supporting me for chair was the test of whether you still intended to broaden your coalition and maintain the party's commitment to left/center/right alliances," Fulani wrote. Rejecting her, Fulani said, shows Buchanan is trying to move the Reform Party "in a direction that most American independents do not support."
Bay Buchanan said, "It simply could not and would not be with the best interest of the party to support her for chair."
Fulani also pointed to the contentious party meeting in Nashville, Tenn., earlier this year in which former party chairman Jack Gargan was ousted. Buchanan's refusal to support her in trying to get Gargan re-elected as chairman "demonstrated that you were more than willing to 'stick it' to your friends as well as your enemies to achieve ... your own ends," Fulani wrote.
In an interview Monday, Fulani said she met with Buchanan on Thursday and discussed her feelings about the campaign, specifically whom he might choose as a running mate. Fulani had hoped he would consider choosing someone more liberal to show his commitment to a "left-right coalition." Buchanan did not show any interest in that, she said.
"Obviously, Pat has chosen to run his campaign in a much more narrow way to appeal to the right and he has not taken the effort to reach out beyond his iitial base despite his initial interest in doing so," Fulani said.
But Buchanan, after leaving the Republican Party to run for the Reform Party's nomination, wooed Fulani with his support of same-day voter registration, political reform, campaign finance reform, opposition to some international trade agreements, and foreign policy.