President Obama on Tuesday used his veto power to block the Keystone XL pipeline, saying he did so because Congress' attempt to force the project on the American people circumvented the executive branch's authority to make the call on construction after a full review process.

The next step by the president should be to officially reject the project because it is a bad idea.

Sen. Ed Markey summed up the matter well.

"We should not help some of the dirtiest oil in the world to be funneled through our country like a straw, just so much of it can be exported to foreign nations. That is a bad deal for our country, and a dangerous proposition for our climate," said the Massachusetts Democrat.

The legislation, if it became law, would authorize TransCanada Corp. to build the pipeline from its tar sands fields through Montana and South Dakota, connecting with existing pipelines in Steele City, Neb. All told, the 1,700-mile pipeline would pass through six states on its way to refineries on the Gulf Coast, including passing over the shallow Ogallala Aquifer, which runs under eight states and is critical to Great Plains agriculture.

Production of oil from tar sands is the dirtiest method in the world, creating excessive greenhouse gases and requiring almost as much energy to produce as will be available when the oil is burned. It is far more efficient at generating profits for oil companies than producing fuel.

Critics of the veto say TransCanada will continue to produce the oil for world markets anyway, using a more dangerous method of train transport - rail. That may be true, or it may be that without the pipeline, and with the recent downward pressure on oil prices, oil from tar sands may prove too costly to produce.

In any event, the U.S. should not support a project that will accelerate climate change just because someone else may do it.

President Obama says his administration is still weighing the pipeline's merits. But if Obama really wants to make fighting climate change a main focus of his last two years in office, as he has stated, his final decision would appear obvious - no.