Washington (CNN) President Donald Trump's acknowledgment that he discussed former Vice President Joe Biden in a July call with Ukraine's president has intensified scrutiny on his interactions and decisions on Ukraine.

The growing controversy stems from a whistleblower complaint that deals, at least in part, with a phone call Trump had with Ukrainian President Volodymyr Zelensky on July 25. A transcript of the conversation released by the White House shows Trump repeatedly pushed Zelensky to investigate former Vice President Joe Biden and his son, Hunter.

There is no evidence of wrongdoing by either Joe or Hunter Biden.

Even before the whistleblower complaint was made available to lawmakers, House Speaker Nancy Pelosi on Tuesday declared Trump had betrayed his oath of office and announced she was opening a formal impeachment inquiry into the President.

Below is a timeline of recent key events and stories surrounding Trump, Ukraine and the intelligence whistleblower.