Some of Jackson's successors made no use of the veto power, while others used it intermittently. It was only after the Civil War that presidents began to use the power to truly counterbalance Congress. Andrew Johnson, a Democrat, vetoed several Reconstruction bills passed by the "Radical Republicans." Congress, however, managed to override fifteen of Johnson's twenty-nine vetoes. Furthermore, it attempted to curb the power of the presidency by passing the Tenure of Office Act. The Act required Senate approval for the dismissal of senior Cabinet officials. When Johnson deliberately violated the Act, which he felt was unconstitutional (Supreme Court decisions later vindicated such a position), the House of Representatives impeached him; he was acquitted in the Senate by one vote.
Try to answer this question if possible (otherwise reply "unanswerable"): How many of Johnson's fifteen vetoes did Congress override?
unanswerable