韓国では大統領選挙がたけなわです。throw one's support behind~は「〜を支援する」という意味です。supportをthrowするというのは実に英語的な発想です。まあ、「weightを投げる」（throw one's weight around、「威張り散らす」）という比喩表現があるくらいなので驚きはしませんが...。（EnDough）
Presidential race goes head-to-head
Two main presidential hopefuls are running neck and neck ahead of the Dec. 19 election the latest polls showed after a popular independent candidate bowed out of the race.
The polls suggested a tight race between the ruling conservative and the liberal opposition after Ahn Cheol-soo, a left-leaning software mogul with no party affiliation, left the campaign in a bid to consolidate liberal votes.
A poll conducted Nov. 24 by the JoongAng Ilbo newspaper showed the ruling New Frontier Party’s Park Geun-hye with 44.7 percent support, marginally ahead of Moon Jae-in’s 41.3 percent.
The survey was held after Ahn — who enjoyed huge popularity among young and some previously undecided voters — announced his departure Nov. 23 and threw his support behind Moon from the liberal opposition Democratic United Party.