Answer:
The Vice President serves as a "back-up" to the President, who also serves as the Head of State (President of the Senate, presides over joint Congress sessions).
In the presidential line of succession, the Vice President is the second in command.
Texas was annexed by the United States in 1846 and war broke out again with Mexico, Lamar joined the U.S. Army. He fought in the battle of Monterrey and helped organize a municipal government in Laredo. In his later years, Lamar traveled, wrote poetry, and spoke out in support of slavery in the South.