So what if it turns out that volunteers at one Obama rally barred two young Muslim women in "hijab" headscarves from sitting behind the candidate? That's just what happened at an event in Detroit this week, triggering anger from the Muslim community and, four days later, personal apologies to the women from Obama himself when media coverage of the snub had escalated.

The incident highlights the importance in modern politics of getting your image right (and the pitfalls of going too far). The Republicans were pioneers of this when, at their 2000 presidential convention, they elevated black and Hispanic faces onto the stage. (What the viewing public didn't see was that behind the cameras, the hall was a sea of white people with barely a person of colour in sight. The public also didn't see the Texas convention bow down their heads in prayer when an openly gay congressman came on stage to give a speech.)

The image of this year's Republican candidate, John McCain, is still a work in progress. At his best, the Arizona senator looks relaxed and confident when he engages with voters at freewheeling meetings on the hustings. At his worst, McCain can look stilted as he struggles with the teleprompter at scripted events.

For Obama, an image of professorial cool is giving way to a more presidential air, and the media are feeling the effects as what little access we had to the Democratic candidate is restricted further. That's in keeping with the evolution of previous White House candidates as the general election season draws nearer. But Obama knows he must also stay connected to the supporters who have propelled his astonishing rise. I suspect his campaign volunteers will be told in no uncertain terms to go easy on the hijabs in future.