From my understanding, it is largely the Bush Tax cuts expiring, and a large decrease in government spending.
Overall, it will be a good thing in the long run. Government spending is always funded at the expense of private entities. It can be funded directly through taxation, or indirectly through loans from various institutions which crowds out the private sector. A reduction in government spending means (a) less taxation (but this is not the case), or (b) an increase in the availability of money for the private sector (this is the case).
Since the private sector now have more money to borrow (since the government spends less, thus needs to borrow less, leaving more funds for private sector), this will result in a much better allocation of resources. Since the private sector is the sector which generates all the wealth in the US, this will increase people standard of living over time as there as been an expansion in wealth. An expansion in the private sector will also increase competition and put downward pressure on prices, increasing the purchasing power of consumers, and again, their standard of living.
The increase in taxation however will reverse this effect as it diverts wealth away from the private sector towards the public sector, and the opposite of the above will be true. That said, since the deficit will decrease, it means that there will be a net movement of 'money' if you like towards the private sector, so overall, in the long run, there will be a benefit to the country.
The short-term is less fruitful however. Government spending cuts to any industry always results in unemployment. Although the unemployment will result from the relatively less productive sectors, for, without government assistance, they would never have emerged in the first place; their existence has crowded out more productive and independent private sector entrepreneurs.
TLDR: Not so good for short term as unemployment will increase. Good for long-term as the public sector will downsize, and the private sector will expand, resulting in an increase in the standard of living for all.