"Overreaching and defying Congress will not be rewarded or succeed," Wednesday's letter from six state Attorneys General read in part.
The controversial pipeline must be shut down and emptied within 30 days as officials review its environmental impact, a district court judge ruled.
U.S. energy trading experts said Monday's first-ever oil futures crash below $0 does not mean that Americans will suddenly be paid to fill up their cars' gas tanks.
Russia is the world's biggest energy exporter, but for the past four years, sagging oil prices have severely hurt its economy. Trump's actions could reverse that.
A U.S. spy satellite captured images of Chinese ships secretly selling oil to the pariah state 30 times in the past three months.
The country's oil supply is far greater than previously reported.
Brent crude oil appears to continue rising through what has been a volatile week for the industry.
Under the circumstances, the Kremlin is unlikely to continue its costly war with Ukraine.
Oil prices have slid more than 25 percent so far this year
Crude oil futures tumbled 6 percent on Monday, reaching their lowest in nearly seven years.
The last time energy was this cheap, Eisenhower was president.
A U.S. and EU oil embargo would cripple Russia overnight as it relies largely on pipelines to the West.
Norwegian boss, who started in February, set to "move along" when takeover deal closes around early 2016.
Oil prices remain roughly 50% below their peak from the middle of last year.