What does "lethal aid" (4th paragraph) mean?

Context>>>>>>>>>
Democrats in the House of Representatives are holding hearings to investigate whether Trump improperly pressured Ukraine to investigate a political rival, former Vice President Joe Biden, and his son Hunter, who sat on the board of a Ukrainian energy company. The House could vote on impeachment later this year, which would trigger a trial in the Republican-controlled Senate, where a conviction and ouster seem unlikely.

The confirmation of a quid pro quo, or favor for a favor, would bolster Democrats' arguments that Trump misused his office.

In a written statement, Mulvaney later accused the media of misconstruing his comments. But his remarks at the White House, made while the president was traveling in Texas, tied action on the DNC server to the decision about the aid.

"Did he also mention to me ... the corruption related to the DNC server? Absolutely. No question about that. But that's it. And that's why we held up the money," Mulvaney told reporters in the White House briefing room after saying Trump had also been concerned that European nations were not providing lethal aide to Ukraine.

Later in the day, in an effort at damage control, Mulvaney said the withholding of aid was related strictly to Trump's concerns about corruption and the fact that other nations were not providing financial support to the country.

"Let me be clear, there was absolutely no quid pro quo between Ukrainian military aid and any investigation into the 2016 election. The president never told me to withhold any money until the Ukrainians did anything related to the server," he said in the written statement released by the White House.