Of course Polk also sent the troops into the disputed teritory without Congressional Authorization. Polk of course knew it would provoke a fight. It raises a question of Presidential War Powers. Can the President intentionally provoke a war without Congress' consent?
Well, he certainly can.
Polk did. Roosevelt was trying to provoke a war with Germany when Pearl Harbor took him off the hook.
Some (especially on this forum) argue that Lincoln did essentially the same thing.
He did.