WPP said its investment management business Kantar had bought Benenson Strategy Group, a US strategic research and consulting firm founded and run by President Obama's top campaign pollster.Chief Executive Officer Joel Benenson, who set up the company in 2000 with Chief Operating Officer Carl Rossow, will remain at the helm with the rest of the senior leadership team. The New York-based company was founded in 2000 and has advised 11 Prime Ministers and Presidents worldwide. It ran the research and polling program for President Obama's 2008 and 2012 campaigns and made revenues of $15.6m in the year to June 30th. The deal is the latest in a string of acquisitions announced by WPP this summer.Shares in WPP were up 19p at 1,210p at 11:29 on Friday.TB