Sept. 16, 2008, was a flashpoint in the financial crisis for many safety-conscious investors. That was the day that the Reserve Primary Fund "broke the buck," meaning its net asset value fell below $1 per share.
Retail investors who were already spooked by tumbling markets sought to bail from the fund and wound up getting back about 97 cents on the dollar.
Investors turned away from money market funds after the crisis, and low interest rates deterred them from pouring cash back into these supposed safe havens.
For instance, at the end of 2010, money market funds had an annual negative net flow of $359 billion, according to research firm Morningstar.
Net flows were back in positive territory at the end of 2017, at $110.3 billion.
New rules went into effect in 2016, permitting retail and government money market funds to maintain a stable $1 NAV, but requiring institutional funds to have "floating" NAVs like other mutual funds.
The new regulations also allowed fund managers to assess redemption fees or even temporarily suspend redemptions in order to prevent investors from yanking out cash en masse.
"The money market fund turmoil caused all kinds of havoc," said Cox. "It's not impossible for it to happen again, but the risk is significantly reduced."