Question

When was the last time a senator was expelled from the u s senate?

Answer 1

Since 1862, no Senator has been expelled, though there were multiple efforts over the course of time but never were they successful.  In 1797 a Senator was expelled for the charges of treason and then in 1861-62 fourteen more met the same fate for joining and helping Confederacy in the Civil War.
So its been about 155 years :)