The currently anonymous whistleblower is expected to testify to Congress about the complaint, which alleges that Trump abused his office to get Ukraine to investigate political rival and 2020 Democratic presidential contender Joe Biden, the former US vice president. Trump denies there was any wrongdoing or quid pro quo.
Depending on how the impeachment process goes, the Democrats and Republicans could both benefit.
The Democrats will investigate other administration and cabinet officials as part of the probe.
Investigating other officials could prolong the impeachment story, perhaps beyond the end of any presidential impeachment.
Impeachment in November, heightening partisan divisions, could coincide with a federal government shutdown, exacerbating it.
If Trump were removed, Vice President Mike Pence would become president immediately.
