Stocks fell on Wednesday after President Donald Trump said the United States will build a wall along the Mexican border even if it means shutting down the government.
If Congress does not reach a funding deal that the president signs into law by a Sept. 30 deadline, the government will shut down. Lawmakers are also facing a vote to increase the borrowing limit by the end of September.
Senate Majority Leader Mitch McConnell said on Monday there is "zero chance" the U.S. won't raise the debt ceiling.
"America's not going to default," he said at an event in Kentucky.
Meanwhile, the last government shutdown, in 2013, lasted about 2.5 weeks and did not have a big impact on the economy, according to Michael Feroli, chief U.S. economist at JPMorgan.
However, he said a failure on the debt ceiling may be a different story.
"We've never had the debt ceiling go past its drop-dead date, so it could potentially be quite disastrous for the economy," he told "Closing Bell," pointing out that it depends on how long it goes on.
While he doesn't think it's going to be an issue, he said, people need to keep it in mind.
Pethokoukis also isn't betting on a government default, putting the chances of Congress not hiking the debt limit to "pretty darn close to zero."
However, he said a government shutdown for a small amount of time is likely and he wouldn't be surprised by a temporary resolution on funding or the debt ceiling.
— CNBC's Jacob Pramuk contributed to this report.