Politicians have floated the idea of minor sanctions, such as travel restrictions on more Russian officials, but these are unlikely to have any effect, experts told CNBC.
Ineffective, or otherwise, new sanctions may be on their way, according to some international observers.
As violence intensifies in the far east of Ukraine, "Brussels and Washington will hold Russia chiefly responsible, and they will expand existing sanctions in the coming months. This will not, however, change Putin's policy or calculus in Ukraine," Alexander Kliment, director of Russia and EM research at Eurasia Group, wrote in an email to CNBC.
One way to bolster existing sanctions' impact would be a law that permanently codifies them. Many expect such a bill to be passed by the U.S. Congress—especially when Republicans take control of the Senate in January—but it is unclear whether President Barack Obama would sign it.
"Once you pass a law, it's hard to repeal a law," Jensen said.
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But even that move could be ineffective without coordination with Europe—which is far from a sure bet.
"If the U.S. does it, it doesn't mean the Europeans will follow suit. And as long as it's just us, the action remains weak," Goodrich said. "You have to get the Europeans on board, and it's not an option for them."
The best course of action to keep economic pressure on Russia, both Goodrich and Jensen said, would be to maintain the current sanctions for years to come. But Europe may be less inclined to renew its restrictions when they expire next year, they said.
—CNBC's Dina Gusovsky contributed reporting.