AI Overview
Estimates suggest a single nuclear weapon test could cost around $140 million, based on past studies, although the total cost is not precisely known and would also include significant environmental and political consequences.
And he's going to catch a lot of flak against the idea.
AI Overview
Presidential authority and constraints
 Sole authority: The U.S. president, as Commander-in-Chief, has the sole constitutional authority to order the use of nuclear weapons. This includes the ability to order a test, as no one in the military or Congress can legally overrule that order.
Congressional oversight: While Congress does not need to approve the president's order, it does have a critical role through its power of the purse. Restarting nuclear testing would be expensive, and Congress could deny or restrict funding for the necessary preparations and execution.
The Comprehensive Test Ban Treaty (CTBT): The U.S. is a signatory to the CTBT, which bans all nuclear test explosions, but it has not ratified it. Resuming testing would violate the spirit of the treaty and draw sharp condemnation from U.S. allies and the international community. 
Practical hurdles
 Time and cost: It would take an estimated 24 to 36 months to prepare for and execute an underground nuclear test at the Nevada National Security Site. The last U.S. test was in 1992, and the required workforce and infrastructure are no longer fully in place.
 Environmental and safety concerns: Previous testing caused radioactive fallout that resulted in illnesses for many people. Resuming tests would face renewed opposition from environmental and anti-nuclear groups and local residents.
 International reaction: Any decision by the U.S. to resume nuclear testing would likely cause other nuclear powers, such as Russia and China, to do the same. This could destabilize decades of non-proliferation efforts and escalate a new nuclear arms race.