evidence: KYIV — Ukraine’s friends are committed to helping it fortify and prevail against Russia’s full-scale invasion, Secretary of State Antony Blinken declared in a speech in Ukraine’s capital Tuesday, vowing to aid in the Kremlin’s defeat even as Kyiv faces deepening questions about its ability to hold off an assault threatening its front lines. [...] Blinken’s unannounced two-day trip was the first high-level visit by a Biden administration official since Congress last month approved a $61 billion aid package for Ukraine after seven months of obstruction by some Republicans. The visit was intended as a show of solidarity as the Pentagon speeds delivery of air defenses, artillery and other combat equipment in a bid to stabilize Kyiv’s military — and as Ukraine contends with the possibility that it may never regain all the territory it has lost to Russia. [...] Blinken has also been largely preoccupied elsewhere in recent months, focusing on the Middle East since the Oct. 7 Hamas attack on Israel and Israel’s subsequent military operation in Gaza. While lower-level trips to Ukraine have continued, Blinken has visited the Middle East seven times since the fall, a measure of the degree to which regional diplomacy there is now consuming his days. By contrast, he has traveled to Kyiv four times since Russia invaded Ukraine in February 2022.