No, America’s current birth rate is not sustainable for population replacement without immigration. The total fertility rate is below the replacement level of 2.1 births per woman, which could lead to slower economic growth and fiscal challenges, though population growth is projected to continue this century due to immigration. 

Reasons why the birth rate is not sustainable

• Below replacement level: The total fertility rate has been below the 2.1 births per woman needed to replace the population for some time.
• No signs of rebound: Recent trends suggest this is a sustained decline, not just a temporary delay in childbearing, meaning women are having fewer children over their lifetime.
• Projected long-term consequences: A sustained low birth rate could lead to slower economic growth, a shrinking workforce, and increased fiscal challenges for social programs like Social Security. 

How the population is maintained

• Immigration: Immigration is currently offsetting the low birth rate and is expected to be the primary driver of U.S. population growth throughout the century.
• Increased longevity: Longer life expectancies also contribute to population growth, even with fewer births. 

Contributing factors to the declining birth rate

• Economic factors: Rising costs of healthcare and childcare are often cited as contributing factors.
• Cultural shifts: Broader shifts in priorities among younger generations are also believed to be a significant cause.
• Financial challenges: The aftermath of the 2008 financial crash and other economic pressures may have also played a role.