Comment: 25 pages, 5 figuresThis paper posits the decline in market capitalization following a monopoly breakup serves as a means to gauge how financial markets assess market power. Our research, which employs univariate structural time series models to estimate the firm's value without the breakup and juxtapose it with actual post-divestiture values, reveals a staggering drop in AT&T's value by 65% and AMX's by 32% from their pre-breakup levels. These findings underscore the contemporary valuation of monopoly rents as perceived by financial markets, highlighting the significant impact of monopoly breakup on market capitalization and the need for a deeper understanding of these dynamics.