On Wednesday, Federal Reserve policymakers delivered what Wall Street expected: It will commit to a fourth round of quantitative easing or "QE4" in the guise of ongoing $45 billion-a-month Treasury bond purchases. 

This will be combined with the $40 billion-a-month in mortgage security purchases that began under "QE3" back in September. (QE4 will replace the expiring "Operation Twist" initiative, but will be more aggressive since it represents new dollar creation rather than the selling of short-term bonds to buy long-term bonds.)

But here's the kicker: The Fed has replaced its low-rate commitment through 2015 with policy thresholds. Now, it will keep interest rates low unless unemployment drops below 6.5% or inflation rises above 2.5%. Given food and energy supply constraints, inflation could limit the Fed's stimulus sooner than many believe -- forcing the Fed to either abandon its commitment or start raising rates. Here's why: 

Already, the Consumer Price Index is growing at a 2.2% annual rate. The Core CPI, which excludes food and energy, is growing at a 2.0% rate. Also, the Core Producer Price Index is rising at a 2.5% annual rate after posting one of its largest one-month post-recession gains in November.

While food and energy prices will remain volatile and affected by the health of the global economy, the real driver of the recent increase in inflationary pressures has been the rebound in housing. Specifically, the increase in apartment rents as shown below.

After years in the doldrums, household formations are creeping higher again as young adults once again move out on their own. With mortgage credit still tight, people are competing for attractive rental properties.

Should this measure continue to rise, the Fed could be forced to pull back on stimulus to honor its new commitment well before hitting its unemployment target.

That's because, despite a drop in the unemployment rate from 8.3% to 7.7% over the last few months, as I discussed in a recent post, the drop has been driven largely by a reduction in the size of the workforce rather than an overwhelming surge of new jobs. If the economy actually improves, these people will reenter the workforce and put upward pressure on the unemployment rate.

The other option is that the funny business with the employment numbers continues, in which case on current trajectory we will hit the 6.5% unemployment rate in mid-2013 -- forcing the Fed to pullback when the real, underlying jobs picture remains difficult.

So the overall takeaway: The Fed will continue to buy bonds at an $85 billion-a-month rate; it will be slightly more aggressive in its creation of new dollars; and the establishment of policy thresholds increases the chance that higher inflation, rather than a stronger job market, is the catalyst that forces it to pullback.

Stocks and other assets are performing their usual post-Fed spasms. Once things settle down, I expect traders will connect the dots and view today's events as a net negative for the cheap-money, higher-stocks game we've been playing since 2008.

Combined with new recessions in Europe and Japan and the unresolved "fiscal cliff" here at home, I expect stocks to fall from their current levels in the weeks to come. In fact, we could be on the cusp of a new bear market, according to some research I'm seeing. I'll have more to say about that next week.

For now, I recommend investors book long profits and move to cash.

Be sure to check out Anthony's new investment newsletter, the Edge, and his money management service, Mirhaydari Capital Management. A two-week free trial has been extended to MSN Money readers. Click the link above to sign up. Mirhaydari can be contacted at anthony@edgeletter.c​​om and followed on Twitter at @EdgeLetter. You can view his current stock picks here. Feel free to comment below.