Senate Foreign Relations Committee ranking member Bob Menendez (D-N.J.) on Tuesday questioned Vice President Pence and Energy Secretary Rick Perry regarding their travel to Ukraine as the White House faces scrutiny for its dealings with the country. 

The questions in letters Menendez sent to Pence and Perry centered around Pence’s canceled trip to Ukrainian President Volodymyr Zelensky's inauguration and Perry’s trip in his place.

"Given your role as the leader of the official United States delegation to the inauguration, and the White House’s recent release of evidence that President Trump requested that Ukraine’s government investigate his domestic political opponent, your insight into the U.S. delegation’s trip is of particular interest to the Senate Foreign Relations Committee," Menendez wrote in his letter to Perry.

Menendez asked the Energy secretary about who asked him to lead the delegation and why, as well as whether he was asked to convey "President Trump’s desire for assistance in investigating one of his political opponents or their family members, or unsubstantiated theories related to Ukraine’s involvement in the 2016 U.S. election."

The Democrat asked Pence why his trip was canceled and also questioned him on his travel to the country in September.

"You met with President Zelensky in Warsaw, Poland. When asked by a reporter on that trip whether you could ‘assure Ukraine that the hold-up of that money has absolutely nothing to do with efforts, including by Rudy Giuliani, to try to dig up dirt on the Biden family,’ you did not answer the question,” he wrote to Pence.

“As the summary of the call with President Zelensky demonstrates, President Trump requested a foreign government help investigate his domestic political opponent. While I hope that he was alone in making such an inappropriate request, your statements regarding your discussions with Ukraine officials raise questions whether you may have helped carry that message,”  he added.

Menendez requested that the administration officials answer his questions by this Friday.

The inauguration trip is mentioned in the recently released whistleblower complaint in which Trump is accused of pushing Zelensky to investigate Democratic presidential candidate Joe Biden for Trump's benefit. The president has denied wrongdoing.

"On or around 14 May, the President instructed Vice President Pence to cancel his planned travel to Ukraine to attend President Zelenskyy' s inauguration on 20 May," the complaint said, citing U.S. officials. "Secretary of Energy Rick Perry led the delegation instead."

"According to these officials, it was also 'made clear; to them that the President did not want to meet with Mr. Zelenskyy until he saw how Zelenskyy 'chose to act; in office. I do not know how this guidance was communicated, or by whom. I also do not know whether this action was connected with the broader understanding, described in the unclassified letter, that a meeting or phone call between the President and President Zelenskyy would depend on whether Zelenskyy showed willingness to 'play ball,' " it continued.