It's to do with very long term ties between groups in both countries on both the centrist left and the right. Small numbers of democrats have helped in UK elections, again as unpaid individuals.
Contacts and links at conferences and think tanks are common/shared USA/UK and again across the spectrum - and ongoing.
Some Republicans are currently decrying the 100 low level volunteers who have gone in their own time and are unpaid (staying in democrat activists homes)
But some Republicans are happy to look the other way when things like this happen: look the other way look at what is going - on as regards paid involvement in the states by a UK MP:
“Farage given free team of US PR advisers by former Bannon aide’s firm
Reform UK leader received support for his American activities after becoming an MP but has not declared the services as a benefit”
“Nigel Farage has used a team of three US advisers to help him with “perception management” and public relations in America, as well as with settling a $3,500 hotel bill this summer, new documents show.”
.....the MP for Clacton has been assisted at least 15 times....
According to the documents, CapitalHQ was hired to take on activities for Farage including “promotion, perception management, public relations, speeches, appearances, communications, travel, accommodation and logistics and other political activities in furtherance of political interests of the foreign principal”. It describes his address as the House of Commons in London
www.theguardian.com/politics/2024/oct/17/farage-given-free-team-of-us-pr-advisers-by-former-bannon-aides-firm
www.theguardian.com/politics/2024/oct/17/farage-given-free-team-of-us-pr-advisers-by-former-bannon-aides-firm