Senators on both sides of the aisle responded quickly to the U.S. Army Corps of Engineers’ decision to halt construction of the Dakota Access pipeline beneath a Missouri River reservoir.

This newest development in the months-long Standing Rock saga has left protesters optimistic about pushing for an alternative pipeline route, but they remain wary of a policy reversal once Donald Trump takes office in January, according to The Associated Press.

The Corps on Sunday refused to approve an easement that would have allowed part of the pipeline to be built under Lake Oahe, potentially threatening the Standing Rock Sioux tribe’s drinking water and cultural sites.

Following the decision, Democratic North Dakota junior Sen. Heidi Heitkamp criticized the Obama administration for delaying action on pipeline construction and voiced concerns over the safety of protesters during North Dakota’s bitter winter.

“This administration’s delay in taking action — after I’ve pushed the White House, Army Corps, and other federal agencies for months to make a decision — means that today’s move doesn’t actually bring finality to the project,” Hetikamp said in a statement. “The pipeline still remains in limbo.”