The trade deficit remains the soft underbelly of the US economy.

贸易赤字仍是美国经济的软肋。

《牛津词典》

I know where his soft underbelly is, and that's his material possessions.

我知道他的弱点是什么，是他的财产。

《柯林斯英汉双解大词典》

You need to find the soft underbelly of your opponents, and then beat them.

你需要先找到对手的软肋，然后再击败他们。

youdao

"That is the soft underbelly of Kabul, " said a coalition special operations forces official in Afghanistan.

WSJ: Karzai Says Taliban 'in Service to America'

But worries persist that Yudhoyono's nation is a soft underbelly in resistance to a possible avian-flu pandemic emanating from Asia.

FORBES: Magazine Article

Nobody is much discussing the soft underbelly of the Sprint situation as it fantasizes about becoming the final consolidator in the wireless space.

FORBES: Ergen Throws DISHwater on Sprint/Clearwire Soap Opera