I watched it. It was clearly a mistake he meant to say Iran. Even Vance was confused by what he said.
Who are Israel’s proxies? “Iran and its proxies” is a very common line used to describe the various organisations with links to and support from Iran and Waltz was nervous at the start of the debate and stumbling his lines.
But the expansion of Israel and its proxies is an absolute, fundamental necessity for the United States to have the steady leadership there
This have absolutely zero sense if he wanted to say "Iran". Expansion of Iran would be absolute fundamental necessity for the United States??? In all other times when he speaks about Iran he's total hawk and sometimes even already speaks like there is open war between US and Iran.
But the expansion of Israel and its proxies is an absolute, fundamental necessity for the United States to have the steady leadership there.
Even assuming it really was brainfart, dude who make multiple such brainfarts in a single sentence, entirely changing the meaning of his speech shouldn't be even village post worker, not to mention Vice President of USA.
And considering what he said exactly fits and is consistent with both US decalrations and actions, this wasn't a brainfart, it was something much worse for them: a moment of sincerity.