This article is from the archive of our partner National Journal

Republicans backing Keystone XL, the controversial oil pipeline at the heart of Capitol Hill battles this week, have long touted polling that consistently shows clear public support for the project.

But two new polls dent those arguments just as the years-long political and lobbying battle over TransCanada Corp.'s pipeline comes to a head this week with a Senate bill that would approve the project.

An NBC News/Wall Street Journal survey released Tuesday shows that 41 percent favor construction of the pipeline to bring crude oil from Canadian oil sands to Gulf Coast refineries, while 20 percent oppose it and 37 percent did not know enough to weigh in.

An ABC News/Washington Post poll unveiled Monday, meanwhile, asked whether Congress should pass legislation approving the project or wait until the Obama administration completes its review. Sixty-one percent favored completing the review before deciding, while 34 percent backed authorizing construction now.

The question was not a gauge of support for the project itself. Instead, it was about process, asking whether Keystone should be approved right now or whether the administration's review to determine if it's in the "national interest" should proceed.

The White House has long maintained that the lengthy review of the project should be allowed to play itself out and that Congress should not step in.

President Obama has recently made comments critical of the pipeline's benefit and has threatened to veto the Senate bill, but he has not tipped his hand on whether he plans to approve or reject the project.

The debate is intensifying in Congress even as gasoline prices have been dropping sharply in recent months. The average nationwide price of regular gas is $2.05 a gallon, compared to $2.43 a month ago and $3.28 at this time last year, according to AAA.

To be sure, the pro-Keystone coalition--Republicans, business groups, and some Democrats--can point to a substantial number of polls that show public support for the pipeline over time.

For instance, the respected Pew Research Center has been polling on Keystone for several years. A late 2014 Pew survey showed 59 percent in favor compared to 31 percent in opposition, although Pew noted that support had fallen from 66 percent in March 2013 (declining support from Democrats and independents accounted for the drop).

And how questions are worded matters a lot in polls. An NBC News/Wall Street Journal poll conducted in November asked about Keystone differently than the one released Tuesday. The pollsters listed a series of actions the newly elected Congress could take. In that survey, 54 percent approved of authorizing Keystone, while 16 percent were neutral and 28 percent opposed it.

The Senate is to begin voting Tuesday on amendments to the Keystone legislation. The Obama administration review, meanwhile, is restarting thanks to a Nebraska Supreme Court decision this month that upheld the pipeline route through the state.

This article is from the archive of our partner National Journal.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.