The reasons for investors to be pessimistic are beginning to pile up just as quickly as the market has been sliding down. A once-pristine fundamental backdrop suddenly looks tarnished, as worries accelerate that economic growth may have peaked, political headwinds are forming, and rising interest rates will stand in the way of future fiscal stimulus from the Trump administration. While stocks had been staging a mild relief rebound in November, Monday's sharp decline shows that the market remains temperamental. All it took was a negative headline for Apple about iPhone demand and news about a lingering regulatory issue for Goldman Sachs to send Wall Street into another tailspin. The market's vulnerability has become a common theme among market pros warning their clients not to take too much risk in the current climate. "Ongoing risks keep us cautious and we continue to recommend that investors pare back risk if their equity holdings are above longer-term strategic allocations," senior strategists at Charles Schwab warned clients in a report Monday. "Economic and earnings growth rates may be peaking, while the labor market continues to tighten. This mix contributes to higher wage growth, possibly higher inflation and related uncertainty with regard to Fed policy." Those are but some of the risks on invevstors' minds these days.

Talk around the Street has ranged from the dangers that wobbly fundamentals pose to the weak technical backdrop that includes a dangerous double-top chart formation in the . Schwab's team pointed out there remain reasons for hope, particularly from seasonal trends that back a strong November and a historical pattern behind positive results in the third year of presidential election cycles. "But given the uncertainties that still exist and the potential slowdown in both earnings and economic growth, we continue to recommend a fairly cautious approach to investing, including discipline around diversification and rebalancing," the paper, co-authored by Liz Ann Sonders, Brad Sorensen and Jeffrey Kleintop, advised.

The bear case

The factors lining up against the market are formidable: fears over growth in China and around the world, rising interest rates, the ongoing tariff battle between the U.S. and its trading partners, midterm election results that saw the Democrats take the House, slumping oil prices caused in part by a drop-off in demand and the likelihood that U.S. corporate profits, while stellar, are peaking and likely will taper off in 2019. "Unlike 2016, there are no more tax cuts to salivate over and the deregulation momentum is going to now slow, or maybe stall, in the House," David Rosenberg, chief economist and strategist at Gluskin Sheff, said in his daily note Monday. "Rare is the day when the stock market goes down in the lead-up to Thanksgiving – and if it does, that indeed will be a very bearish signal."

November is generally a solid if unspectacular month for the markets, averaging a 0.9 percent gain over the past decade, ranking it fifth overall, according to FactSet. November, though, has not been negative since 2011, the longest winning streak for any month. However, there are some cracks in market behavior. Rosenberg pointed to rising trading volume amid a market decline Friday, which he said shows "that institutions are now more willing to sell on strength than buy the dips." On the more fundamental side of the ledger, a deceleration in China reflected in tumbling energy prices is just the latest sign of a global economy that is putting on the brakes. Meanwhile, the U.S. and China continue to apply duties to imports that, while not yet showing up in corporate earnings, are a concern into 2019 absent a thawing in tensions. "So much of it is going to depend on the tariff stuff," said JJ Kinahan, chief market strategist at TD Ameritrade. "The market hates uncertainty. That's the biggest cause of uncertainty. You've got the election settled, hopefully you have that settled by the end of the month."

The bull case