You may see that written in the Constitution. But the US Senate is on record as not seeing it there. I'd thought like you until I read some history in the run up to Clinton's impeachment. The operative clause is Article II, Sect. 4:
The president, vice-president and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.
The Senate ruled that Senators weren't "civil officers" of the United States and thus weren't subject to impeachment. I don't know their reasoning, nor whatever meaning "civil officers" had in English common law, which I presume should have provided such definitions back in 1797. Thus I don't know enough to know whether their ruling was justified or just arrogant, but it's not been challenged since. You can only expel a US Senator. I DO recall, and suspect you will also, Dungheap Harkin at the start of Clinton's "trial" getting Rehnquist to rule essentially that the Senate could set its own rules for it. Perhaps that applied in 1797 as well.
Personally I'd like to impeach Bill Clinton from the civil office of "former President." Remove his staff, his pension, his SS protection (Clinton said it wasn't needed and time limited it for every President after him) and reduce him to hiding behind Hillary's skirts. Officially shun him for a legacy. None of the political excuses then against convicting him apply now, and most of those then voting against conviction now admit he was guilty.
Sorry for the mistakes from previous post, I'm a little tired.
Senators can be impeached as can all govt officials. And it just takes a majority of the "House of Representatives" PRESENT for the vote to do so. Clinton was Impeached!
It just takes 2/3 vote of the Senators PRESENT to remove from office! It's called a trial when it gets to the Senate. Bill Clinton and Andrew Johnson were the only 2 Presidents to be Impeached by the House. They had trails in the Senate.
Johnson was one vote short of being "removed from office" in the Senate. Clinton was between 9 to 15 (?) votes from being removed from office in the Senate, so it was not close.
A lot of freepers get this mixed up.