You could say U.S. Sen. Mary Landrieu’s bid to get the lame-duck Democratic Senate to approve the long-delayed Keystone XL pipeline was a Hail Mary. Or maybe the whole episode seemed like a vintage Keystone Kops movie.

Pick your cliché to describe Landrieu’s futile attempt to change the dynamic of her runoff contest against U.S. Rep. Bill Cassidy. Everyone else has.

Whatever you call it, no matter how hard Landrieu contends that she accomplished something by simply landing an elusive floor vote — an inside baseball argument if ever there was one — Landrieu’s late-inning maneuver merely wound up highlighting the larger forces at play. Keystone aside, most of those forces are working against her as she tries to hold on to her seat for a fourth term, just as they have been throughout the campaign season.

After picking up just 59 of 100 votes — and yes, in today’s dysfunctional Senate, an 18-point win counts as a loss because the threat of filibuster has become the rule rather than the exception — Landrieu said it was an example of her intent to “fight for the people of my state until the day that I leave.”

But Landrieu’s been making that argument since day one, often using far better examples than her failed advocacy of a project that doesn’t even go through Louisiana.

She didn’t need Keystone to prove that she’s focused on delivering for Louisiana. She’s got a long record on that front, including the cancellation of nearly $400 million in federal community disaster loans for various local government agencies after Hurricane Katrina and major legislation to direct offshore revenues and BP fines to the state. She’s also already well-established as an advocate for the industry, much to the irritation of her party’s environmental wing.

But none of that kept 58 percent of primary voters from choosing a Republican, leaving her with just 42 percent, a huge gap to close in just four weeks.

Nor did Landrieu — who, win or lose, will forfeit her Energy Committee chairmanship in January when the Republicans take over the Senate — show herself to be indispensable to Keystone supporters.

Instead, she just drew attention to the fact that she couldn’t get that one last Democratic vote she needed to pass the bill. As if to rub it in, Cassidy himself sponsored the successful companion bill in the House, and soon after the Senate vote, incoming Majority Leader Mitch McConnell took to the mic and promised to try again in the upcoming term, when the measure will almost certainly pass.

Landrieu’s gambit was clearly aimed at highlighting her willingness to break with Obama, another major plank in her campaign since the beginning. But the primary results here, not to mention the final counts in other moderate-to-conservative states, suggest that many of this year’s voters aren’t satisfied with situational opposition.

Cassidy, of course, has built an entire campaign on catering to Obama critics. He’s repeated his go-to contention that Landrieu votes with the president most of the time so often that he doesn’t even bother to explain it anymore. His latest ad features a shorthand that could pass for parody if the words weren’t coming out of Cassidy’s own mouth: “And remember, Mary Landrieu, Barack Obama, 97 percent.”

That Cassidy’s come this close to unseating an effective incumbent with that approach — and without bothering to talk about what he’d hope to do in the last four of the term’s six years, after Obama leaves office — points to Landrieu’s biggest obstacle of all.

Sure, Louisiana used to elect members of Congress with little regard to party. But those days are clearly gone; Louisiana is as red a state as there is, and it’s voting accordingly. This was a partisan race through and through, and it continues to be in its closing weeks. Perhaps even more so, as the Republicans bring in a host of 2016 presidential aspirants, from Rand Paul to Rick Perry to Marco Rubio, all hoping to help Cassidy close the deal.

Contrast that with Landrieu’s inability to find that one last Democratic vote to land the Keystone victory. The takeaway there is that the party is cutting its losses and moving on.

Honestly, it’s hard to imagine how passing Keystone could have shifted these dynamics much, particularly if Obama had vetoed the bill, as he’d hinted he’d do.

But trying so hard and then not passing it? That just highlights the fact that the always-endangered Landrieu really is in her toughest fight yet.

Stephanie Grace can be contacted at sgrace@theadvocate.com. Read her blog at blogs.theadvocate.com/gracenotes. Follow her on Twitter, @stephgracenola.