The Clinton Foundation lists the Brazilian construction firm OAS and the InterAmerican Development Bank (IDB) as donors that have given it between $1 million and $5 million. Those relationships are worth learning more about.

OAS has been in the news because it is caught up in a corruption scandal centered on Brazil’s state-owned oil company, Petrobras. In November Brazilian police arrested three top OAS executives for their alleged roles in a bribery scheme involving inflated contracts and kickbacks. OAS denies the allegations....