The last poll I saw shows his approval rating at 39%. For comparison, the lowest approval rating (from Eisenhower to Obama) for a President after his first 100 days was Bill Clinton at 55%. Reagan and Bush Sr were tied for lowest initial approval rating at 51%. (Source)

At this point, Trump basically has a core group of supporters who would still approve of him even if he held a press conference to announce his "secret silent partner" and had Putin walk onstage.