Van Buren's opposition to immediate annexation cost him the support of many pro-slavery Democrats. In the weeks before the 1844 Democratic National Convention, Van Buren's supporters anticipated that he would win a majority of the delegates on the first presidential ballot, but would not be able to win the support of the required two-thirds of delegates. Van Buren's supporters attempted to prevent the adoption of the two-thirds rule, but several Northern delegates joined with Southern delegates in implementing the two-thirds rule for the 1844 convention. Van Buren won 146 of the 266 votes on the first presidential ballot, with only 12 of his votes coming from Southern states.