WASHINGTON (AP) -- Forget Robert Mueller.

The greatest threat to President Donald Trump's re-election bid may not be the slew of investigations closing in on his Oval Office but a possible economic slowdown. And the president knows it.

The Dow Jones Industrial Average fell again Monday, the latest dip in the roller coaster markets amid the strain of Trump's trade war, rising interest rates and worries about a slowing global economy.

Trump, who has tied his political fortunes to the stock market in an unprecedented fashion, has nervously watched Wall Street, keeping an eye on the cable television ticker and barking at his aides for updates. And while he continues to talk up America's financial might, he has repeatedly and publicly rebuked the chairman of the Federal Reserve for interest rate increases he feels could slow the economy.

Trump made his feelings clear again Tuesday, a day before the Fed is expected to raise its key interest rate for the fourth time this year.

"I hope the people over at the Fed will read today's Wall Street Journal Editorial before they make yet another mistake. Also, don't let the market become any more illiquid than it already is. Stop with the 50 B's. Feel the market, don't just go by meaningless numbers. Good luck!"

He said Monday on Twitter that "It is incredible that with a very strong dollar and virtually no inflation, the outside world blowing up around us, Paris is burning and China way down, the Fed is even considering yet another interest rate hike. Take the Victory!"

Throughout Trump's term, the economy has been strong. And while the president credits his aggressive tax-cut package and deregulation efforts, the gains in fact began under President Barack Obama.

Optimism about the economy has cooled somewhat this fall as Trump's trade fight with China rattled the markets.

Fond of citing job statistics and market reports, Trump has appeared highly attuned to the shift. After unnerving much of the global financial system by imposing tariffs, Trump seemed eager to ease anxiety recently, striking a trade truce with China after a dinner meeting during an international summit in Argentina. And when that move only briefly buoyed confidence, Trump set off on an erratic bout of tweeting that rocked the markets even more.

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First Trump declared himself a "Tariff Man," promising to inflict as much economic pain as possible — a move that horrified investors. A day later he sought to minimize the anxieties, saying there were "very strong signals" that China was negotiating in good faith.

"Not to sound naive or anything, but I believe President Xi meant every word of what he said at our long and hopefully historic meeting," Trump tweeted.

Stocks fell again Monday as both the Dow and the S&P 500 are on pace for their worst December performance since 1931, when they were battered during the Great Depression. As investors turned to an upcoming meeting of the Federal Reserve, its chairman, Jerome Powell, has repeatedly been the target of Trump's wrath, as the Fed has been raising interest rates to make sure that the lowest unemployment in nearly five decades does not start pushing inflation higher. Arguing that the rate hikes hamper economic growth, Trump has openly questioned Powell's leadership.

"I think the Fed is making a mistake. They are so tight. I think the Fed has gone crazy," the president said in October.

No longer tweeting much about the stock market, Trump has criticized Powell privately as well and has told confidants that he understands that a recession would be perilous for a president who once mused about the Dow hitting 30,000. (Its record was 26,828 in October.) Although Trump is not seriously considering making a change at the Fed, he has repeatedly insisted that his businessman background allows him to understand the economy more than Powell, according to four White House aides and outside advisers who were not authorized to discuss private conversations and who spoke on condition of anonymity.

"He thinks his legacy is going to be the guy who rebuilt and revived the U.S. economy. He's totally focused on that," said Stephen Moore, a former Trump campaign adviser and visiting fellow at the Heritage Foundation. "He understands that if the economy remains strong, he'll be re-elected. He's completely focused on the economy. He does follow the stock market, he does follow the stock reports, he does follow the jobs report."

Democrats considering challenging Trump in 2020 have begun putting forward their own economic plans. But a senior White House official said Trump remains confident in the economy, citing low unemployment numbers, GDP growth and growth in manufacturing jobs, among other indicators.

The official, who wasn't authorized to speak publicly, said Trump is watching the indicators closely and is regularly briefed by Larry Kudlow, director of the National Economic Council; Treasury Secretary Steven Mnuchin; and Kevin Hassett, chairman of the Council of Economic Advisers.

"The American economy is booming," Kudlow told The Associated Press. "While economies around the world are struggling, our economic fundamentals are incredibly strong."

Trump is right to worry about how an economic slowdown could affect his presidency. Bill Clinton aide James Carville's famous mantra during the 1992 presidential campaign was: "It's the economy, stupid." And the nation's financial health is often key to a president's re-election chances.

The last two presidents who failed to be re-elected, Jimmy Carter and George H.W. Bush, were primarily done in by faltering economies, said presidential historian Douglas Brinkley.

"It's hard to convince the public to give you another chance if the economy is not doing well," said Brinkley, a professor at Rice University. He suggested that even voters who do not like Trump's personal behavior "tolerate him because they think he is good for Wall Street and jobs. If there is an economic downturn, that is going to take a devastating effect on him."

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