What legislative policies exist to prevent, prepare for, respond to, and recover from a WMD attack at a seaport? Are these current policies sufficient to secure and protect US Ports? Explain.

The most important legislation regarding these concerns is the 2002 Maritime Transportation Security Act (MTSA), which President Bush signed into law in November 2002 as public law (PL 107-295). Although the law was passed largely in response to the 9/11 attacks, it had been in the works long before. A ten-year retrospective analysis was presented in a 2012 report to the US Congress. The MTSA includes the authorization to fund the US Coast Guard and the Customs Service for port-related matters, many of which are concerned with "weapons of mass destruction" (WMDs) and other weapons.
Specifically, the MTSA authorizes the following: the purchase and maintenance of screening equipment to detect WMDs, nuclear materials, potentially harmful chemical or biological agents, and other conventional weapons; improved methods for inspection of merchandise on any vessel headed toward or arrived at a US port; and improved labeling and tagging of containers, throughout its supply chain, to track and detect hazardous or radioactive materials. In addition to detection, the MTSA authorizes development and installation of tools that would mitigate the consequences of a terrorist act at a port of the United States (e.g., sensors for predicting the dispersion of radiological, chemical, or biological agents).
The entire law is available as a PDF on the Department of Homeland Security website here.
One important feature that was put in place through the 2002 MTSA was the creation of area maritime security committees (AMSCs). Composed of federal, state, local, and private representatives, the committees identify and address port vulnerabilities and facilitate the sharing of information about port security issues.
It has been widely argued that additional funding is needed to secure the ports. Numerous organizations--including, but not limited to, the US military--have called for increased funding for port security. For example, in 2018 the American Association of Port Authorities (AAPA) supported an increase in the the Port Security Grant Program. The AAPA has also published position papers favoring improved infrastructure through increased funding for Customs and Border Protection (CBP) and the Coast Guard.
https://www.aapa-ports.org/advocating/content.aspx?ItemNumber=21149

https://www.hsdl.org/c/tl/maritime-transportation-security-act-2002/