With overwhelming majorities, both the House and the Senate passed a bill on sanctions. The bill completely tied the hands of the president, requiring him to seek congressional permission before reducing sanctions. This was a clear attempt to usurp the president's authority to determine and conduct foreign policy. For the Never-Trumpers this had to look like a win-win scenario, for them.
If the president rejected the bill and refused to sign it into law on the ground that it was clearly unconstitutional, the Never-Trumpers would have had a Christmas, Thanks Giving and the Fouth of July all-in-one. They could have overthrown the presidential veto by virtue of their overwhelming majorities and construed his behaviour as proof of Russia, Russia, Russia, and instituted impeachment proceedings, a purely political decision. The coup d'etat complete. Pence installed as president, normalcy resumed. If the president signed the bill, Congress took control over foreign policy. As I said, heads Congress wins, tails Congress wins. That's the way the anti-Trumpers expected it to go.
However. President Trump, who the Never-Trumpers like to portrary as a political oaf, did not fall into the trap. Instead, he signed the bill. But, he also signed a Statement. The Statement makes it perfectly clear that he considers the bill to be unconstitutional and lays out the basis of the legal case, including the citation of cases decided by the Supreme Court. The statement was evidently written by Constitutional lawyers. This move completely outflanks the Congressional anti-Trumpers. It denies the bill any validity and it denies the anti-Trumpers the opportunity to construe his behaviour as proof that he is Putin's puppet. It also paves the way for the Supreme Court to strike down the bill as unconstitutional. The president has thus turned a purely Congressional matter into a legal matter, a legal matter the executive cannot lose.
More than this, the Russia, Russia, Russia hysteria is simply not working on Trump's supporters in the country (according to MSNBC et al because they are too stupid to understand). These are people many of the Representatives and Senators who voted for the bill will have to answer to in the mid-term elections. Many of those voters are going to be wondering why Congress wants to tie the hands of the president, specifically why Congress is determined to prevent the president from improving relations with Russia. It will require spin of a very high order to answer such questions in a manner that does not look like passing the bill was driven by a desire to delegitimatise and undermine and disempower the president.