Depending on what policies are enacted by the people in government can determine whether or not the economy does well. This might be because the amount of jobs have increased or decreased or whether or not a person saves or is able to pay taxes. More directly a business could choose to send jobs elsewhere if they have to pay more taxes for staying in the country.
Between the Federal Reserve, the Treasury and Congress, the United States government has a fair amount of control over the US economy. The biggest example can be seen with the Federal Reserve, which has control over several interest rates in the US. Their action, or inaction, has the ability to cause a domino effect and strengthen or weaken the US economy.
The government sets taxes and terrifs, the minimum wage, and regulations on industries to name a few things that it does. It also is one of the largest employers in the US and helps to create jobs and to set wages and salaries for these jobs. These people also buy more or less depending on how much they make.
On the one hand, the government sets the bar in terms of policy and regulation but it will never really control the economy. The economy will never be tamed by anyone entity simply because its gigantic; it can only be guided and even then its not without difficulties. All the facets of government can change, aid, and influence the economy but not in ways they would have envisioned. Often times policies that was believed to be the answer, to bend the economy to success lead the US to near calamity. Why? Because they failed to realize that control is non-existent, especially in economics. You can only attempt to shape it, hope it works and change with the times. The reason government failed: because it relied on sheer fortune and nothing else.
The government tries to control the economy. In fact, it tries so hard that is has a large organization created that spends all their time doing it. But, ultimately, it all comes down to buyers and sellers. A government cannot control a man selling his used toaster, and likewise cannot control the macroeconomic side of that.