In election campaigns, presidents often promise more of everything (that is, more guns and more butter). what would those elected president fulfill that promise?

More economic growth

Explanation:

The government has three sources of income: taxation, debt, and currency printing.

Economic growth would help increase income in with each of the three sources.

More economic growth means that people and firms are earning more money, therefore, they can be taxed more.

If the country has a high growth rate, it's credit rating will probably be good, and obtaining debt will probably be cheaper and easier.

If the economy is growing, the central bank can print more money without causing excessive inflation.