It was cannabis Wednesday in Congress, where lawmakers gave the strongest support yet for ending the country's laws prohibiting marijuana use.

In the strongest sign yet that deciders in Washington may soon be ready to undo federal marijuana prohibition, both Democrats and Republicans voted to approve three pro-cannabis budget amendments — and came very close to approving a fourth in support of recreational marijuana.

Bipartisan votes approved amendments forbidding Justice Department officials from interfering in state-legal medical cannabis operations, industrial hemp programs, and laws that allow citizens to access products high in less-psychoactive cannabis compound CBD (cannabidiol).

This was easily the biggest day for cannabis in Congress to date — and it led one pro-marijuana lawmaker to predict that federal cannabis prohibition will be done within five years.

The pro-marijuana amendments are all meant to limit the Drug Enforcment Administration's reach by cutting its budget. All told, about $23 million...