John R. Bolton, President Trump’s former national security adviser, has knowledge of “many relevant meetings and conversations” connected to the Ukraine pressure campaign that House impeachment investigators do not yet know about, his lawyer told lawmakers on Friday.

The lawyer, Charles J. Cooper, made that tantalizing point in a letter to the chief House lawyer in response to House committee chairmen who have sought Mr. Bolton’s testimony in their impeachment proceedings but expressed unwillingness to go to court to get an order compelling it…

Mr. Bolton “was personally involved in many of the events, meetings, and conversations about which you have already received testimony, as well as many relevant meetings and conversations that have not yet been discussed in the testimonies thus far,” Mr. Cooper wrote in the letter.