• US and Ukraine discuss security guarantee amid controversy over peace plan.
• Plan includes demands that Kyiv cede territory to Russia and ban Ukraine from joining NATO.
• US and Ukrainian officials indicate progress, but details remain to be worked out.
• Security guarantees crucial for Ukraine's safety, according to experts.
• US and European involvement in guarantee is essential for credibility.
• Russian President Putin may try to hold agreement hostage to demands.
• Congress may play key role in ratifying security guarantee.
• Army Secretary Dan Driscoll emerges as key player in negotiations.
• Ukraine's military cap at 800,000 sparks concerns about long-term sustainability.

The US and Ukraine's discussion of a security guarantee may indicate a shift in the conflict's dynamics, but the outcome is far from certain. The involvement of the US and Europe in guaranteeing Ukraine's safety could strengthen the country's position, but Moscow's skepticism suggests that a comprehensive agreement may be difficult to reach. The Army Secretary's role in negotiations highlights the administration's unconventional approach, but the need for a credible guarantee remains a pressing concern.