The sources say that part of these discussions involves implications, such as concerns about executive privileges, if current White House employees like Bolton and Mick Mulvaney, acting White House chief of staff, are forced to testify publicly.
The testimony of these authorities could add important revelations to the investigation, due to the first-hand knowledge of the government's relations with Ukraine.
"There are a number of contingencies. We are prepared," said the senior government official. The sources would not disclose what the contingencies are.
Senate minority leader Chuck Schumer and Senate Democrats pressured the Senate to hear four witnesses, including Bolton and Mulvaney, and to subpoena documents that the White House blocked from the House's impeachment investigation. But Senate majority leader Mitch McConnell says he has enough Republican votes to support rule-making without Democratic support.
The White House expects Schumer to have no votes on the first day of the Senate trial on Tuesday, but there is the potential for him to get enough Republicans on his side to vote for witnesses after both sides present their cases.
The main focus of the White House, according to the sources, is to ensure that Schumer does not get the 51 votes needed.
"You would have to convince 51 senators to say that the Senate is going to relinquish executive privileges. That is a very high order," said one of the sources.
McConnell's organizing resolution for the Senate trial postpones the question of witnesses until both sides present their opening arguments and there are 16 hours of questions for senators, to be asked by Supreme Court judge John Roberts, who is presiding over the judgment. .
At that point, the resolution includes a proposal in which the Senate would vote on a motion on "whether to consider and debate under the rules of impeachment any motion to summon witnesses or documents".
Democrats oppose McConnell's agenda, which House Democratic advisers said on Monday as an effort to "hide the president's misconduct in the dark of night."