וְהָיָ֤ה יְהוָה֙ עִמּ֔וֹ בְּכֹ֥ל אֲשֶׁר־יֵצֵ֖א יַשְׂכִּ֑יל וַיִּמְרֹ֥ד בְּמֶֽלֶךְ־אַשּׁ֖וּר וְלֹ֥א עֲבָדֽוֹ׃
And the LORD was with him: whithersoever he went forth he prospered; and he rebelled against the king of Assyria, and served him not.
From David to Destruction
Chizkiyahu HaMelech’s two overly bold actions are his rebellion against Assyria (Melachim II 18:7) and his alliance with the Babylonians (Melachim II 20:12-13). Likewise, Yoshiyahu acts too boldly when he seeks to halt the Egyptian army’s travel through Eretz Yisrael (Melachim II 23:29).
Rashi
In what do you trust It is written (I Kings 18:5): “He trusted in the Lord God of Israel,” and it is also written there: (verse 7) “and he rebelled against the king of Assyria.” Therefore, he asked, “In what do you trust” that you have rebelled against me?
From David to Destruction
Melachim II 18:7 states that “Hashem was always with him [Chizkiyahu]; he was successful wherever he turned; he rebelled against the king of Assyria and would not serve him.” Notice that the rebellion is presented separately from the description of Chizkiyahus’s wise and successful actions. This indicates that the rebellion was neither wise nor successful.