A government shutdown at midnight looks likely. What it means for Social Security and unemployment checks, the IRS, markets and more.

1. A partial government shutdown is likely, with 80% chance predicted. 2. Senate failed to pass funding bill, fueling shutdown concerns. 3. Historic analysis shows S&P 500 generally rises during shutdowns. 4. Shutdown effects may be minimized by essential services remaining operational. 5. Mass layoffs could differ this time, impacting market sentiment.