A hangover from the crisis The recession of 2008-9 was caused by the worst financial crisis since the Great Depression of the 1930s. Maybe something about financial crises makes recovery from a downturn all the more difficult.

During the recent crisis, many feared another Great Depression would follow. We averted that catastrophe, but the anxiety may linger, causing businesses to be reluctant to borrow to finance risky investments and banks reluctant to finance them. The good news is that hangovers eventually dissipate, but patience is required.

Secular stagnation Lawrence H. Summers, former economic adviser to President Obama, has suggested that the problem predates the recent financial crisis. He points to the long-term decline in inflation-adjusted interest rates as evidence of reduced demand for capital to fund investment projects. He cites several reasons for the change, including lower population growth, lower prices for capital goods and the nature of recent innovations, like the replacement of brick-and-mortar stores with retail websites. The result, he says, is secular stagnation — a persistent inability of the economy to generate sufficient demand to maintain full employment.

His solution? More government spending on infrastructure, like roads, bridges and airports. If the government takes advantage of lower interest rates to make the right investments in public capital — admittedly a big if — the policy would promote employment in the short run as projects are being built and make the economy more productive when they are put into use.

Slower innovation Robert Gordon, author of “The Rise and Fall of American Growth: The U.S. Standard of Living Since the Civil War,” believes the pace of innovative activity has declined. Previous generations introduced electricity, indoor plumbing and the internal combustion engine. This generation’s innovations, like the smartphone and social media, are just not as life-changing.

This theory is the most pessimistic. If he’s right, we may have little choice but to get used to slower growth.

Policy missteps When Barack Obama took office in 2009, the economy was in the midst of the Great Recession. President Obama’s advisers relied on standard Keynesian theory when they proposed a large increase in government spending to energize the economy. The stimulus package was the administration’s first economic policy initiative. As the economy recovered, the administration supported tax increases to shrink the budget deficit.