WASHINGTON — The Biden administration has been enlisting one emissary after another to try to convince Senate Republican leader Mitch McConnell to help raise the federal debt limit. It’s not working.

Despite high-level conversations, including a call from Treasury Secretary Janet Yellen, McConnell is telling all who will listen that it’s up to the Democrats, who have narrow control of Congress, to take the unpopular vote over federal borrowing.

McConnell’s stance is deepening a political standoff and risking turbulence in the financial markets that could ripple into the broader economy. His refusal to rally Republican votes leaves Democrats with only tough choices as they rush to ensure the nation does not default on any of its accumulated debt, which now stands at $28.4 trillion.

President Joe Biden and the Democratic leaders, House Speaker Nancy Pelosi and Senate Majority Leader Chuck Schumer, are scheduled to speak Thursday afternoon. While there is little doubt the Democrats will vote to allow additional borrowing, the path ahead is uncertain and potentially treacherous.

“We are working; there are a number of different options,” Schumer told reporters earlier this week at the Capitol. “We will do it because its imperative to do it. And Leader McConnell, as I said, is playing dangerous political games by not stepping up to the plate.”

The showdown is sparking a fiscal battle that is reminiscent, but different, from those that have set Washington and Wall Street on edge at times over the past decade. Unlike the brinksmanship of past battles, this one is unique in that there is no deal to be brokered — McConnell simply will not participate.

Lawmakers appear to have only a few weeks to devise a plan for approving the federal government’s debt limit before the U.S. Treasury is forced to delay or miss payments.

Stocks and bonds have been relatively calm recently, indicating investors expect Washington will ultimately reach a deal on the debt ceiling. The S&P 500 remains within 2% of its record set two weeks ago, and prices in the bond market are moving more on reports about the economy and inflation. But the ride could get bumpier in coming weeks.

Because they’re seen as the world’s safest possible investments, U.S. Treasury bills and bonds form the bedrock for financial markets. So a default on the U.S. debt would quickly cascade through markets around the world.

Treasury spokeswoman Lily Adams said in statement Thursday, “Secretary Yellen will continue to talk to Republicans and Democrats about the critical need to swiftly address the debt ceiling in a bipartisan manner, to avoid the catastrophic economic consequences of default.”

The debt limit caps the amount of money Treasury can borrow to keep the government running and pay its debts.

Once a routine task in Congress that brought grumbling from lawmakers but not high-stakes opposition, votes to increase or suspend the debt ceiling are now often contentious.

The debt ceiling vote became a political weapon in 2011, wielded by a new class of tea party Republicans eager to confront the Obama administration as the debt load ballooned during the Great Recession. Prolonged and heated discussions during that crisis risked a federal default, a first in the modern era, but eventually a deal was brokered to begin to curtail spending levels.