Bob Menendez claimed vindication today after the Department of Justice dropped the remaining corruption charges against him, but it might not be entirely over yet. After an adverse ruling from the presiding federal judge in the case, prosecutors decided that they had very little hope for success gaining convictions on the remaining counts. And they were probably correct:

Last week U.S. District Judge William Walls threw out some of the bribery charges on the grounds that prosecutors had failed to show that about $660,000 in political contributions from Melgen to help benefit Menendez’s 2012 reelection campaign were part of any bribery scheme.

The mere fact that some of the money arrived around the same time that Menendez took actions that could benefit Melgen was not enough to prove a “quid pro quo” arrangement, Walls said.

“Given the impact of the Court’s Jan. 24 Order on the charges and the evidence admissible in a retrial, the United States has determined that it will not retry the defendants on the remaining charges,” the Justice Department said in a statement.

That was at least a small surprise for the prosecution. The quid pro quo standard got a lot tougher after the Supreme Court decision that overturned the convictions of former Virginia governor Bob McDonnell. The McDonnell decision set a requirement that both official acts of the office and payment directed for those ends had to be present for bribery and corruption.

The defense raised this issue during the first trial to dismiss on that basis, and at first, Walls appeared to take it under consideration. Eventually, Walls dismissed the defense motion, relying on the “stream of benefits” to rule that it was the jury’s job to decide whether the gifts were a direct payment thereof. Had Menendez gotten convicted, that would almost certainly have been the main point of attack on appeal.

Walls must have had second thoughts about “stream of benefits” theory, raising the bar for conviction so high that the DoJ would have needed a “smoking gun” to win — an e-mail discussing payoffs, or an eyewitness to the transactions to make the explicit bribery case. Having neither, prosecutors have little choice but to walk away. Salomon Melgen also benefits from this dismissal, but he’s also already been convicted of Medicare fraud and will likely spend several years in prison anyway.

Menendez isn’t off the hook entirely, however. The Senate Ethics Committee has reopened its probe into the smelly arrangements and gifts between Menendez and Melgen, which could result in a recommendation for expulsion. That sets up a very interesting conundrum for Senate Democrats, who didn’t even bother to have the Ethics panel investigate Al Franken before they chased him out of the Senate. If the Ethics committee returns a conclusion that Menendez engaged in corruption, will the same Senate Democrats who hailed their “zero tolerance policy” on personal behavior outside the Senate (in Franken’s case) apply it to corrupt behavior in office, too? Or will Menendez get a pass as his colleagues try to bury it in a difficult midterm in the Senate?