The Libre Initiative, an advocacy group affiliated with mega-donor Charles Koch’s political network, will announce Monday four endorsements in key congressional races. Libre is endorsing Reps. Maria Elvira Salazar (R-Fla.), Monica De La Cruz (R-Texas) and Juan Ciscomani (R-Ariz.) for reelection and Nevada GOP Senate candidate Sam Brown, who is challenging Sen. Jacky Rosen (D).…