Midrasch zu Jirmejahu 11:5

Rabbi Yehuda ben Rabbi Simon began: “He said: I will hide My face from them” (Deuteronomy 32:20). [It is analogous] to a king’s son who went out to the marketplace and struck but was not hit, demeaned but was not demeaned, and he went running up to his father. He [his father] said to him: ‘What do you think, that you are honored because your own honor? You are honored only because of my honor.’ What did his father do? He repudiated him, and no one paid any attention to him [the son]. So, when Israel departed from Egypt, dread of them fell over all the nations, as it is stated: “Peoples heard, they were agitated; terror gripped the dwellers of Philistia. Then the chieftains of Edom were confounded, trembling gripped the powers of Moav, all the dwellers of Canaan dissolved. Dread and fear fall upon them” (Exodus 15:14–16). When they began transgressing and performing evil deeds, the Holy One blessed be He said to them: What do you think, that you are honored due to your own honor? You are honored only due to My honor. What did the Holy One blessed be He do? He repudiated them a bit, and the Amalekites came and confronted Israel, as it is stated: “Amalek came and waged war with Israel in Refidim” (Exodus 17:8). In addition, the Canaanites came and confronted Israel, as it is stated: “The Canaanites heard […and waged war with Israel]” (Numbers 21:1).
The Holy One blessed be He said: You have no faithfulness, you are not true to your word, you are erratic, as it is stated; “As they are an erratic generation, children in whom there is no trust [emun]” (Deuteronomy 32:20). It is written amen. When the prophets would bless them, not one of them began to say amen until Jeremiah said it, as it is stated: “I responded, saying: Amen, Lord” (Jeremiah 11:5). At that time, the Holy One blessed be He said: You are erratic, you are bothersome, you are recalcitrant; to eliminate them is impossible, to return them to Egypt is impossible, to exchange them with another nation is impossible…

They are "turncoats" (hafachpechanim), they are "runabouts." "sons without emun": You are sons without emunah (faith). You stood before Mount Sinai and said (Shemoth 24:7) "All that the L-rd spoke we will do and we will hear." I, too, said to you (Psalms 82:6) "You are angels." But since they said of the golden calf (Shemoth 32:4) "These are your gods, O Israel," I, too, said of you (Psalms, Ibid. 7) "but like men will you die." I brought you into the land of your forefathers and I gave you the Temple. I said to you: You will never be exiled from it. But since you said (II Samuel 20:1) 'We have no part in David," I, likewise, said to you (Amos 7:17) "And Israel will be exiled from its land." R. Dostai says: Read it not ("sons) without emun; but "without 'Amen.'" They did not want to answer "Amen" after the prophets when they blessed them. And thus is it written (Jeremiah 11:5) "in order to fulfill the oath that I swore to your forefathers to give them a land flowing with milk and honey, as this very day." And not one of them opened his mouth and answered Amen, until Jeremiah came and answered Amen, as it is written (Ibid.) "And I answered and said: 'Amen, O L-rd!'"