A spokesman for Ms. Sinema said she had participated in fund-raising for the Democratic Senatorial Campaign Committee but declined to say where or provide any additional details. One person briefed on the matter said an event had occurred in Paris. It was not clear whether her trip to Europe was at the urging of the party committee…

Although political campaigns and parties cannot raise money from foreign nationals, American citizens living abroad can and do regularly contribute.

Ms. Sinema’s office declined to say how long she would be abroad, what countries she was visiting, how the trip was being paid for and whether she was doing any additional fund-raising for her own campaign. Her political team had reached out to set up meetings in London and Paris, according to two people familiar with the matter.

John LaBombard, a spokesman for Ms. Sinema, said she remained engaged in the negotiations in Washington.