True, NOT FORMER OFFICERS.
The part that you are not seeing is that the Constitution grants the power of impeachment as a “sole” power to the House. For all practical legal purposes, this means that the House gets to define what is and is not an impeachable offence.
I have no doubt that the House might/probably will adopt an interpretation that they can impeach (at any time) for an “offense” that occurred DURING when the person held the office. However, that is playing with fire.
If that interpretation were to be adopted, ANY former officer (Hillary Clinton, John Kerry, Obama, etc) could be impeached for any offence that occurred while they were in office. Use that against one party, and the other will use it back when they cycle into power.
Very slippery slope if they go down that path.