In the strange world of politics, one might agree with a bill(a proposed law), and still veto it for political reasons. A veto (the noun) is a blockage. Thus to veto something is to prevent it from going forward, which in the case of a bill means to prevent the bill from becoming law.
The President could veto a bill based on the language and not the content. Or for this bill, he could veto it because he believes it unconstitutional.
<<Please keep to the linguistic issues in this forum - avoiding political comment.