President Obama and other politicians are urging a massive expansion in government spending, ostensibly to help the economy recover. This Keynesian endeavor is supposed to boost growth by "priming the pump" by means of circulating extra money through the economy. Yet the notion that bigger government leads to more growth is theoretically unproven: any money that the government "injects" into the economy with new spending (or tax rebates) must first be borrowed and diverted from private use. The economic pie gets sliced differently, but it is not any bigger.
The real-world evidence is similarly unfavorable to Keynesianism. Huge increases in government spending under both Hoover and Roosevelt did not help the economy during the 1930s, and more recent Keynesian initiatives; Gerald Ford's rebates in the mid-1970s, Japan's stimulus efforts in the 1990s, and President Bush's rebates in 2001 and 2008.