Edit - I looked it up.  Prevailing opinions say, being impeached by the house, but not being removed in the senate trial will not prevent Potus running, but I am not sure what ppl were referring to about ability to get on the ballot? Perhaps if impeachment 'trial' is underway, you can't add name? (Searching).  Also, as we have seen, major issues around calling impeachment a crime vs a political hit job with the exception of an obvious crime with no benefit to nation or party.  So far,  https://www.quora.com/Can-a-president-run-for-reelection-after-impeachment If their is a ballot issue while under an impeach trial, this would explain why the dems want witnesses - to stall past the ballot add date. The other argument is that Dems never wanted witnesses, and if denied, they and MSM would smear POTUS during the campaign 24/7  - Look, we could not have witnesses in the house or senate, its a cover up.  In their mind, they may consider it a win eitherway with or without witnesses as they know POTUS would not have been prosecuted so its still a cover up to push. If the ballot date was near, they likely wanted witnesses to stall it out. Amazing how precise they can flip and project their crimes onto repubs.