The president spoke to 19 congressmen from Texas to encourage them to vote for a bill. Since four of the 19 congressmen went on to vote for the bill, it is clear that the president persuaded those four to vote the way they did.
The argument above assumes that the only reason the four congressmen voted for the bill was due to the president's persuasion. However, it is possible that there could be other factors that influenced their decision. To determine if the assumption is valid, we need to evaluate whether there were any other external factors or reasons that may have influenced the congressmen's votes.
