He wrote about this on his page on Twitter.

“As president of the United States, I had and have every right, perhaps even a duty to investigate corruption, and that would include asking or proposing that other countries help us!” He pointed out.

As the President of the United States, I have an absolute right, perhaps even a duty, to investigate, or have investigated, CORRUPTION, and that would include asking, or suggesting, other Countries to help us out!

- Donald J. Trump (@realDonaldTrump) October 4, 2019

Earlier, trump said that, in his opinion, Ukraine should investigate the activities of former vice president Joe Biden and his son Hunter.

On September 25, the White House published a transcript of Trump's conversation with Ukrainian President Vladimir Zelensky.

During the conversation, the Ukrainian leader promised that the new Ukrainian Attorney General will study the situation with the son of former US Vice President Joe Biden.