As the partial U.S. government shutdown dragged into its 19th day, Fitch Ratings warned Wednesday that an extended shutdown might damage the country’s Triple-A credit rating if lawmakers are unable to pass a budget or manage the debt ceiling.

While President Trump spars with Democratic leaders over $5.7 billion for a border wall and funding for nine government agencies, hundreds of thousands of workers are caught up in the shutdown, furloughed or working without being paid, and much of the federal government is paralyzed. The day after Trump took his fight for the wall to prime-time TV on Tuesday, Fitch’s global head of sovereign ratings, James McCormack, said that if the shutdown keeps lawmakers from being able to address the debt ceiling in early March, the inefficiency and ripple effects might do lasting damage to the country’s credit.

“I think people are looking at the CBO [Congressional Budget Office] numbers. If people take the time to look at that you can see debt levels moving higher; you can see the interest burden in the U.S. government moving decidedly higher over the next decade,” McCormack said in an interview with CNBC’s Squawk Box Europe. “There needs to be some kind of fiscal adjustment to offset that, or the deficit itself moves higher, and you’re essentially borrowing money to pay interest on the debt. So there is a meaningful fiscal deterioration there going on in the United States."

If the shutdown is still in effect by March 1 “and the debt ceiling becomes a problem several months later, we may need to start thinking about the policy framework, the inability to pass a budget . . . and whether all of that is consistent” with a Triple-A rating, McCormack said at a later event in London, according to CNBC. “From a rating point of view it is the debt ceiling that is problematic.”

A downgrade in the U.S. credit rating would make borrowing more costly for companies and American households, according to Bill Foster, vice president and senior credit officer at Moody’s, one of the big three credit rating agencies, along with Fitch and Standard & Poor’s. “The U.S. credit rating is the basis or benchmark for so many other lines of credit. If there was a change in the credit rating you’d expect the cost of borrowing to go up, and that would cascade through the economy.”

If the government isn’t reopened by March 1, when the debt ceiling is next scheduled to be addressed, the U.S. Treasury would have to rely on cash-saving tactics — referred to as extraordinary measures — to meet its obligations. If the government is still shut down when extraordinary measures run out, the Treasury would have to start deciding what obligations to meet and face the consequences of putting others on hold.

“Failure to pay Social Security or other benefits on time would have obvious political ramifications. A failure to make interest or principal payments on time — a default — is likely to damage the way the markets view U.S. government debt, perhaps increasing the interest rates that investors demand when they buy Treasury bonds,” experts at the Brookings Institution wrote in 2017 during a past debt ceiling debate.

It’s a default — and the economic nightmare it would trigger — that might ultimately lead to a downgrade for the U.S. credit rating, Foster said, but there’s still plenty of time to avert that kind of crisis. “There’s several months after the March 1 deadline that would allow for negotiations to avoid the default,” he said.

The shutdown is already closing in on the longest in U.S. history, behind the 21-day shutdown under President Bill Clinton that extended from December 1995 to January 1996. In commentary published Friday, according to MarketWatch, Fitch said the fate of the U.S. credit rating depended on whether the impasse behind the shutdown decayed into a “more pronounced destabilization of fiscal policymaking.”

The only time the country’s credit rating has been downgraded was in 2011, when Standard & Poor’s dropped the U.S. rating after the government raised the debt ceiling to allow trillions in additional spending.

“Evidence of greater dysfunction in fiscal policymaking could still contribute to negative pressure on the U.S. rating — (and) this is especially the case as deficits continue to increase,” Fitch wrote in its commentary.

S&P, the other big credit rating agency, did not immediately respond to requests for comment.