lawmakers' pay during a shutdown. The US Constitution currently says they must be paid during a shutdown. The process of passing an amendment to the Constitution is never easy.
A new constitutional amendment would need to be passed by a two-thirds vote in both the House and Senate, and then ratified by three-quarters of the states. Bills and proposed amendments to this effect are often introduced but fail to gain sufficient support.
In this case, it would require the majority of Congress to vote to withhold their own pay. It’s not a surprise that this has never happened.
It should, BTW, not be easy to amend the Constitution. I shudder to think what Trump and this Congress would do to the Constitution, if it was easy.