וְהָיָ֗ה כַּאֲשֶׁ֥ר דִּמִּ֛יתִי לַעֲשׂ֥וֹת לָהֶ֖ם אֶֽעֱשֶׂ֥ה לָכֶֽם׃ (פ)
און עס װעט זײַן, אַזױ װי איך האָב געדאַכט צו טאָן צו זײ, װעל איך טאָן צו אײַך.
Sforno
והיה כאשר דמיתי לעשות להם אעשה לכם, for you will surely follow their religious cult, which will result in your expulsion or death.
Or HaChaim
כאשר דמיתי לעשות להם, "as I meant to do unto them, etc." My commandment was meant for your benefit. Seeing you have not fulfilled it, My commandment remains unfulfilled; I therefore have no choice but to fulfil it in respect of these people you have left in the land.