Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

It's official. We can now add political impasses to the constants in life next to death and taxes.

With little progress on either side of the aisle, it appears we are indeed headed for a government shutdown, scheduled to begin at midnight tonight. Some of my Foolish colleagues would assert that the government shutdown will have little overall effect on the economy of the stock market as a whole. I'd throw myself in the other camp as I sniffed out five ways the government shutdown could harm your investments last week. No matter which side of the aisle you fall on, the stock market tends to dislike uncertainty, which helped push the broad-based S&P 500 (SNPINDEX:^GSPC) lower yet again.

On the economic data front, a positive Chicago PMI data reading of 55.7 was overshadowed by the looming threat of a government shutdown. A stronger-than-expected Chicago PMI reading points to ongoing growth in the manufacturing sector in the Midwest and could signal a stronger recovery than many analysts have predicted. Today, though, that news didn't seem to matter.

By day's end the S&P 500 had flopped for the seventh time in eight days, falling 10.20 points (-0.60%) to close at 1,681.55.

As you might imagine, with state- and federally run health exchanges expected to open for business tomorrow as mandated by Obamacare, health-care stocks were in big focus today. Notably bucking the trend were robotic surgical device maker Intuitive Surgical (NASDAQ:ISRG) and cardiovascular medical device maker St. Jude Medical (NYSE:STJ), which both edged up 2.4% (although Intuitive Surgical edged it by a hair, 2.4% to 2.39%).

The impetus for the move in both stocks was the same: the political impasse over the medical device excise tax in Congress. The Republican-led U.S. House of Representative passed a budget bill that would remove the 2.3% medical device excise tax that St. Jude and Intuitive Surgical have to pay in order to help fund Obamacare and the upcoming Medicaid expansion. The Senate has vowed to kill the House's bill, but it nonetheless represents continued attempts by Republicans to put an end to the medical device excise tax. Even the slimmest chance that this tax could disappear appears to be giving shareholders in both companies a glimmer of hope.

The other big gainer today was biotechnology juggernaut Regeneron Pharmaceuticals (NASDAQ:REGN), which also added 2.4% on a price target upgrade from Oppenheimer to $310 from $300. The move by Oppenheimer comes after Regeneron presented positive phase 3 study data on Eylea for the treatment of diabetic macular edema at two conferences last week. I would in no way argue that Eylea hasn't lived up to (or beyond) every expectation thus far, but I would note that Regeneron's share price probably reflects all of that optimism already and would suggest shareholders remain cautious moving forward.