impeachment investigation. cnn's suzanne malveaux is there. >> reporter: he's the second key witness to go before the house democratic impeachment committees. it will be behind closed doors in just a couple of hours. he is a trump donor. he is a party loyalist. he's also a central figure in the text messages chain that led up to that controversial call. in just hours, gordon sunland, u.s. ambassador to the european union will testify behind closed doors. the first whistle-blower complaint alleges he met with ukraine's president and repo reportedly provided advice to the ukrainian leadership about how to navigate president trump's demands. >> i had a wonderful hour-long meeting with president zelensky that followed on the heels of his telephone call yesterday with president trump. >> he's a hotel tycoon like trump who donated $1 million to his inaugural committee in 2017. last week house democrats