Elected officials and policy advocates are getting increasingly annoyed by Hillary Clinton’s decision to make this nominating contest about her really bad proposal to suspend the gas tax this summer and pay for it with a windfall tax on oil companies.

Today Tom Harkin weighed in on the issue, telling reporters that Congress will not take up this proposal. Even if the gas tax holiday were enacted, Harkin suggested, consumers would not benefit much, and the Iowa Department of Transportation would lose about $75 million in revenues to rebuild infrastructure.

Friends of the Earth Action, which supported John Edwards for president and had been sitting out the campaign since he left the race, today endorsed Barack Obama, largely because of the gas tax issue:

“We endorse Senator Obama because we believe he is the best candidate for the environment,” said Friends of the Earth Action President Brent Blackwelder.  “The ‘gas tax holiday’ debate is a defining moment in the presidential race.  The two other candidates responded with sham solutions that won’t ease pain at the pump, but Senator Obama refused to play that typical Washington game.  Instead, Obama called for real solutions that would make transportation more affordable and curb global warming.  He showed the courage and candor we expect from a president.”

Friends of the Earth Action ran radio and television ads on behalf of Edwards in the early-voting states, and the group is now running this ad supporting Obama:

As I’ve said many times, I would vote for either Obama or Clinton in the general and have no strong preference between the two. I would hate to see Hillary gain the inside track for the nomination through this kind of political posturing, though. It’s such a bad idea on so many levels.

Obama appears to be feeling the heat on this issue. A few days ago his campaign put out a television ad calling the gas tax holiday a “bogus” idea that would just help big oil companies (click the link to view that ad). However, his closing ad in Indiana and North Carolina moves away from that issue to a more general message:

Meanwhile, Clinton seems to think she has hit pay dirt, and has made the gas tax the focus of her closing ad in the states that will vote tomorrow:

For a laugh, I highly recommend this diary by Matt Stoller, CONFIDENTIAL/URGENT POLITICAL PROPOSAL, which skewers Hillary’s proposal on the gas tax by presenting it in the format of those scam e-mails promising to make you rich.

Please put up your predictions for the Indiana and North Carolina primaries in the comments. I say these results will be mirror images of each other: Obama will win NC 55-45, and Hillary will win Indiana by the same margin.