Congress could "bribe" the President to sign a bill by including a Presidential pay raise in it, although the raise would not take effect until after an election (i.e. only works in the president's first term and only if (s)he is reelected). Legally, would that be bribery?
Legally, would that be bribery?
No. It is not conditioned on that individual engaging in conduct to perform the office any differently, and Congress is expressly authorized to do so by law.
Equally important, Congress can't be guilty collectively of a crime, and individual members of Congress are absolutely immune from civil and criminal liability for their official actions under the Speech and Debate Clause of the U.S. Constitution.