John Bolton scheduled to testify in impeachment inquiry next Thursday

It's unclear if he's coming voluntarily or will be subpoenaed

It's also unclear if he will show as White House may cite executive privilege 

He has topped Democrats' wish list for witnesses

Democrats will push him to burn President Trump

Bolton was reported to be frustrated with efforts by Trump's personal attorney Rudy Giuliani to run a shadow foreign policy with the Ukraine

He is in a strong position to answer questions about any quid pro quos