(CNN)Hillary Clinton doesn't just have to worry about Republicans in 2016. She'd better keep an eye on Janet Yellen, too.
Hillary Clinton's 2016 wild card: The Fed
Yellen, the chair of the Federal Reserve, signaled this week that the central bank is heading toward the first interest rate hike since the economic collapse. After six years of near-zero interest rates, an increase -- which could come as early as June or July -- would amount to one of the final chapters of the financial crisis that wrecked the economy.
But for Clinton and congressional Democrats, a rate increase could emerge as an unwelcome wild card in 2016.
The economic turnaround is a critical selling point for Democrats hoping to keep the White House and retake at least one chamber of Congress next year. For the first time since President Barack Obama took office, the labor market is growing at a healthy clip and unemployment has returned to pre-crisis levels. Higher interest rates would increase the cost of everything from home loans to credit card borrowing and could put a damper on economic growth.
Democrats are urging the Fed to take it slow.
New York Sen. Chuck Schumer told CNN it would be "premature to raise rates and slow down the recovery before we've seen wages heading back up."
Ohio Sen. Sherrod Brown, the top Democrat on the Banking Committee, also encouraged caution.
"Given the slack in the labor market and the minuscule increases in the wages for most Americans, the Fed should continue to be patient so as not to choke off the recovery at a time when the stronger dollar is already putting pressure on it," he said.
California Rep. Maxine Waters, the highest-ranking Democrat on the House Financial Services Committee, warned that "the risk of acting prematurely is significant."
Nestled in a marble building facing the National Mall, Fed officials are legendary for their independence from Washington chatter. But the central bank has found itself entangled in politics before.
Jimmy Carter lost his reelection campaign in 1980 amid a Fed crackdown on inflation. After his defeat in 1992, President George H.W. Bush cast blame on then-Chairman Alan Greenspan's management of the Fed.
"I reappointed him, and he disappointed me," Bush famously said.
If Democrats are getting jittery, plenty of Republicans are pleased about the upcoming rate hike. For years, the GOP has blasted the Fed for its massive bond-buying programs and keeping rates near-zero for too long.
"The chorus of complaints has come mostly from Republicans," said Donald Kohn, former vice chairman of the Federal Reserve.
GOP Rep. Bill Huizenga of Michigan, chairman of the Financial Services Monetary Policy Subcommittee, welcomed the change in the Fed's language suggesting a rate increase is in the offing.
"For more than six years, the Federal Reserve has artificially suppressed interest rates to near-zero levels," Huizenga said. "If now isn't the right time to start raising rates, when is?"
Yellen faces the daunting task of overseeing the Fed as it move rates away from near-zero levels. Rates have never been so low for so long and it's impossible to predict what kind of ripple effects raising rates could have on the broader economy.
"There is no way for us to know how this is going to go because we've never been here before," said Lewis Alexander, chief U.S. economist at Nomura.
For Yellen and the Fed, the challenge is to chart a middle path between rate hikes that could halt growth and a status quo that could lead to inflation. Fed watchers say no matter how carefully Yellen and her colleagues execute their next delicate juggling act, the criticism is bound to come from both sides of the interest rate debate.
"The Fed's going to decide what the Fed needs to do and when they do it, one side of the aisle will say: What took you so long? And the other side of the aisle will say: What's your hurry?' said Stuart Hoffman, chief economist for PNC. "And that means the Fed will probably feel that they got it about right."