NEW You can now listen to Fox News articles! Texas Attorney General Ken Paxton on Wednesday demanded Dallas County Sheriff Marian Brown comply with a new state law requiring cooperation with federal immigration authorities, warning he could take legal action if she fails to act. Paxton announced he is investigating Brown over what he described as "sanctuary policies" and sent a formal letter ordering her to pursue a 287(g) agreement with U.S. Immigration and Customs Enforcement, which would allow local deputies to carry out certain federal immigration enforcement duties. The demand stems from Senate Bill 8, which took effect Jan.…