Quoting Commentary for I Kings 22:45

However, his decision to marry his son Yehoram, the crown prince, to Ataliah, the daughter¹³⁰This follows the approach of most Mefarshim, such as Ralbag to Melachim II 8:18; Seder Olam (17) asserts that Ataliah is Yehoshafat’s sister. of Achav and Izevel (Melachim II 8:18) results in an unmitigated disaster, as Sefer Melachim alludes (Melachim I 22:45). Yehoram winds up being a wicked king, who follows in the ways of his wife and in-laws. His son Achazyahu follows this terrible example as well. After the latter’s death at the hands of Yeihu, the evil Ataliah seizes control of the government and heads a reign of terror for seven horrifying years, in which she kills all of her opponents, including her grandchildren (with the exclusion of Yeho’ash).

However, in its summary of Yehoshafat’s reign, after it praises him for “doing that which was proper in the eyes of Hashem” (Melachim I 22:43), Sefer Melachim criticizes Yehoshafat for his failure to remove the Bamot (Melachim I 22:44). Unlike its treatment of Asa’s reign, Sefer Melachim does not close its summary of Yehoshafat’s reign with a positive spiritual evaluation.⁶⁵While Melachim I 22:45 does mention that “Yehoshafat made peace with the king of Israel (Achav),” this cannot be interpreted as praise. As is clear from the rest of Sefer Melachim, Yehoshafat’s alliance with Achav is a dismal failure, as it results in the greater influence of Avodah Zarah in the Yehudah region. The alliance with Achav is formed via the marriage of Yehoshafat’s son Yehoram to Achav’s daughter Ataliah. Yehoram Melech Yehudah is negatively influenced by his wife Ataliah and breaks a streak of sixty-six years of righteous kings. See the later chapter, “Two Tales of Yehoshafat,” for a larger discussion of the outcome of this marriage. Additionally, while the rest of Melachim I 22 does relate more of Yehoshafat’s interactions, it does not explicitly evaluate any of them in spiritual terms. This difference in structure serves to subtly critique Yehoshafat for his failure to remove the Bamot from Yehudah. Additionally, the Navi’s usage of the word “Ach,” “but,” in his description of Yehoshafat’s failure comes to limit the previous accolade’s reach. No such coordinating conjunction is used in the Sefer’s summary of Asa’s reign.