From my reading of the Constitution there is no mechanism to stop an ineligible candidate from running for or even winning the Presidency. It appears that the Congress can challenge the eligility of the candidates only at the counting of the electoral votes as the Democrats attempted with Bush in 2000.
Now since the Treason media has pulled a curtain of silence over this issue the public outrage required to get the Democrats to act responsibly does not exist.
Unless you consider the constitution to be the mechanism, which I do. And citizens have 1000% standing to sue to ensure their constitutional rights are upheld.