The differences between Barack Obama and John McCain became a bit starker this week. McCain supported offshore oil drilling, Obama opposed it. McCain says he’ll take public financing for the general election campaign, Obama is the first presidential candidate since the public finance system was established in 1971 to eschew it.

We thought it would be a good time to reprise how each did in a variety of national polls in the last few days. We’ve included the margin of error, the source and the date it was released.

Obama 51, McCain 36, +/- 4%, Newsweek, June 20

Obama 48, McCain 42, +/- 3%, USA Today/Gallup, June 20

Obama 45, McCain 41, +/- 2% Rasmussen, June 20

Obama 46, McCain 44, +/-2% Gallup Daily Tracking Poll, June 20

Obama 42, McCain 39, +/-3%, Fox News, June 19

Obama 47, McCain 42, +/- 3%, Reuters/Zogby, June 18

All of these polls were done with a methodology that is predicted to be accurate 95 percent of the time – the so-called 95% confidence interval. That means that one out of 20 polls may be wrong, by random chance alone.