What was president lyndon b johnson able to do that president john f kennedy had failed to do?

The correct answer is that he managed to get Congress to pas the tax cuts.

President Johnson managed to get congress to approve a dramatic tax cut for the middle class. President Kennedy had trouble achieving his ideas and passing them through Congress as it was in the Republican majority that did not want to pass the liberal laws Kennedy wanted. After his death the situation changed and his successor Johnson managed to pass the laws Kennedy wanted.

To get congress to approve a dramatic tax cut for the middle class