As The Post's Paul Kane wrote a while back, Democrats could have made it work procedurally, but it would have been difficult from a public relations standpoint:
While Menendez would almost certainly appeal such a verdict, the calls for his immediate resignation would be swift and voluminous. And much has been written about the calamity that his departure would bring on the Democratic Party in this Year of the Deciding Vote....On Oct. 27, 2008, the late Ted Stevens was found guilty on seven felony corruption charges. The Alaska Republican refused to resign, despite a bipartisan chorus calling for him to step down — including the minority leader at the time, Sen. Mitch McConnell (R-Ky.).
Stevens didn't relent, and neither did the last Senate Democrat to find himself in that position, Sen. Harrison “Pete” Williams, who just so happened to also be from New Jersey. Stevens was defeated for reelection within days of his conviction (a conviction that was later vacated), while Williams hung on for 10 months after his conviction before resigning when the Senate was about the expel him.
But keeping Menendez in the Senate might have proven a little more difficult than it seemed — especially given another story that broke Thursday: The sexual assault allegation lodged against Sen. Al Franken (D-Minn.) by model and broadcaster Leeann Tweeden. Franken will now be the subject of an ethics investigation and could face calls for his own resignation. For Democrats, keeping both Franken and a convicted Menendez in their caucus risked an extremely unhelpful narrative.
Menendez has long been a liability for Democrats, given that allegations about his wrongdoing stretch back several years. But at least now if he is convicted, it won't mean Democrats would lose a seat. A Christie-appointed successor would have served only through the 2018 election, when the seat is up for reelection, but it would have at least temporarily given Republicans a crucial vote in a caucus where one vote has often proved the difference between legislation passing or failing. (And it might have offset a potential loss by Republicans in the increasingly perilous Alabama special election featuring Roy Moore.) A Christie appointment could also have given the Republican appointee a leg up on running for the open seat in 2018.
As for that election, Menendez is now faced with a decision about whether to pursue his own reelection campaign. Seeking reelection would seem to give Republicans a chance to run against an embattled incumbent with subpar poll numbers, but New Jersey has proven an extremely difficult place for Republicans to win statewide.
Menendez may have just avoided jail time. But Democrats almost definitely just avoided losing a seat.