Rudy: "I can't tell you if it's 100%" false that Trump threatened Ukraine aid

President Trump's lawyer Rudy Giuliani told Fox Business' Maria Bartiomo Monday that he couldn't assure her "100%" that Trump had not threatened to withhold military aid from Ukraine if the country did not launch an investigation into Joe Biden and his son.

The big picture: Giuliani is at the heart of the Ukraine controversy — which he says involved him asking Ukrainian officials to investigate "Ukrainian collusion" that he claims occurred during the 2016 presidential election — but he acknowledged over the weekend that his request involved Biden.

Watch the exchange:

The big picture, via Axios' Jacob Knutson: House Democrats are now investigating Giuliani's time in Ukraine and whether Trump pressured Ukraine's president to open an investigation into Biden.

• Trump confirmed on Sunday that he discussed Biden with Ukrainian President Volodymyr Zelensky during a July phone call.

Go deeper: What you need to know about the Trump-Ukraine controversy