Sen. Claire McCaskill (D-Mo.) was pretty worried about Donald Trump during the 2016 presidential campaign. "He thinks this is a dictatorship. He doesn't understand," she told Morning Joe about a month before the election. "Just because he says these outrageous things doesn't mean our constitution would allow him to do them."

On Tuesday night, McCaskill had the chance to stick up for those constitutional checks on the Trump team's power to do "outrageous things." Instead, she cast the deciding vote to advance a bill that reauthorizes and expands the power of the federal government—that is, the Trump administration—to snoop on American citizens' private communications.

McCaskill's vote provided the necessary 60-39 margin (Sen. John McCain of Arizona was absent) on the cloture vote, which means there will be only a limited time for debate on the FISA Amendments Reauthorization Act of 2017. Had she voted the other way, it would have opened the door for a filibuster from privacy hawks such as Sen. Rand Paul (R-Ky.) and Sen. Ron Wyden (D-Ore.). For more on what could have happened but didn't, check out Scott Shackford's recap of the drama.

Getting that 60-vote margin required support not just from McCaskill but from 17 other Senate Democrats. Among them: Sen. Bob Casey (D-Penn.), who has labeled Trump "Nixonian" and called for the president's resignation. Sen. Maggie Hassan (D-N.H.), who has said Trump is "dangerous." Sen. Tammy Duckworth (D-Ill.), who has said Trump is not fit to be the nation's commander-in-chief. The list goes on and on.

Sen. Diane Feinstein (D-Calif.) deserves special attention. She wrote an amendment to the FISA bill and tweeted about why it should be considered:

Our amendment would preserve Section 702's core mission of collecting intelligence on foreign individuals abroad while ensuring constitutional protections for Americans. https://t.co/Rtbb448qvL — Sen Dianne Feinstein (@SenFeinstein) January 16, 2018

Then she voted for cloture, killing the opportunity to offer and debate her very own amendment.

Again, just one fewer vote for cloture would have allowed debate to proceed. Feinstein snuffed out her own proposal, along with any amendments that anyone else might have offered.

Republicans get most of the blame for the bill's swift passage. They control the agenda in Congress, and a majority of the GOP in both the House and the Senate have supported reauthorization. But make no mistake: This expansion of the government's powers was a bipartisan exercise.

The same thing happened in the House last week, when dozens of Democrats voted for the FISA reauthorization bill. Minority Leader Nancy Pelosi (D-Calif.) has called Trump "reckless" and "incompetent," but did she vote to give that reckless, incompetent president more power to spy on Americans? You bet.

In the Senate, though, rank-and-file members didn't get cover from their leadership. Minority Leader Chuck Schumer (D-N.Y.) voted against the bill. He disagreed with the six-year span of the reauthorization—that's "too much," he told reporters—and he wanted debate and amendments. He wasn't giving full-throated support to the Paul/Lee/Wyden coalition, but even tacit support matters.

For 18 other Senate Democrats, even that was too much to ask.

McCaskill, I should note, is in a difficult spot. She's one of the most vulnerable Democratic senators up for re-election this year—Trump won Missouri by 18 points—and has already tried to cozy up to Trump on tax reform. Still, her vote on Tuesday is one that should be remembered, particularly when she starts trotting out the inevitable campaign ads arguing that Democratic control of the Senate will be the best check on a dangerous administration.

McCaskill and her colleagues had a chance to check that administration on Tuesday. They failed.