On an otherwise busy day of legislative debate, the Senate ground to an awkward halt for a while May 7 as it was considering a bill to overhaul the nation’s flood insurance program.

The cause? Louisiana Sen. Mary L. Landrieu got into a spat on the Senate floor with fellow Democrat Christopher J. Dodd of Connecticut. She was protesting his move to block an amendment package that she and other Gulf Coast lawmakers had carefully assembled.

Landrieu, who threatened to hold up the bill (S 2284) by reading aloud a litany of e‑mail messages from constituents whose homes were destroyed by Hurricane Katrina, was dissuaded from doing so by Majority Leader Harry Reid, who had stepped in to calm the dispute.

And given the circumstances, it probably won’t be the last time he has to do so.

It is never easy for the conservative-­leaning Landrieu to operate in the Senate’s largely liberal caucus. But it’s even harder now. She faces a tough election this fall, and as one of the most vulnerable members of Reid’s caucus, Landrieu has no wiggle room to help carry water for her party as she tries to stave off attacks that her views, particularly on fiscal and social issues, are far to the left of her constituents’.

In fact, her political survival could easily hinge on how Louisianans judge her work on hurricane recovery efforts, including rebuilding the state’s devastated energy infrastructure.

Landrieu is expected to again test the tolerance of Democratic leaders when they bring to the floor a comprehensive energy bill (S 2991), perhaps as soon as this week.

Landrieu staunchly opposes several aspects of the bill, most notably a plan to roll back $17 billion in tax breaks for oil companies and a proposal to impose a “windfall profits” tax on the largest oil companies.

“I’m not going to spend my time beating up on the oil and gas companies,” said Landrieu. “I normally vote with Republicans on energy matters just because my philosophy is more in line with theirs.”

With a tenuous hold on the majority, Democrats have already tried unsuccessfully to court Landrieu on energy issues.

“We try to take her view into account, but there are other views, too,” said Charles E. Schumer of New York, chairman of the Democratic Senatorial Campaign Committee.

Landrieu, in fact, may vote in favor of a Republican energy proposal (S 2958) that is focused on increasing supply by expanding oil drilling offshore and in the Arctic National Wildlife Refuge.

Reid, D-Nev., meanwhile, has backed away from plans to hold a vote Tuesday on the Democrats’ energy plan, opting instead to offer a scaled-back plan to halt shipments to the Strategic Petroleum Reserve, an issue that unites the parties as gasoline prices rise.

Last December, a package of oil and gas subsidy rollbacks fell one vote short, with Landrieu the sole Democratic opponent. The package was eventually stripped from a larger energy bill.

In March, Democratic budget writers abandoned efforts to protect the oil and gas offsets from filibuster as part of the fiscal 2009 budget resolution (S Con Res 70) because without Landrieu they could not muster the simple majority they needed.

In 2007, Landrieu broke ranks with her party in cases where the majority of Democrats voted together more often than any other Democratic senator except Nebraska’s Ben Nelson, according to CQ’s annual party unity study.

Insiders say that even behind closed doors, Reid does not demand that Landrieu fall in line with the party’s energy agenda, in part because he is sensitive to the political fallout in Louisiana.

“Every now and then, he’ll lean really hard,” Landrieu said. “But they really won’t do that on something like energy with me.”

The fact that they’ve often found an ally in Landrieu has not dampened Republicans’ efforts to oust her in November.

The race, which CQ Politics rates as “Leans Democratic,” could be the toughest yet for Landrieu, who won her first two terms by less than 4 percentage points. Her opponent, State Treasurer John Kennedy, who flipped party affiliations last year to run as a Republican, outraised Landrieu in the first quarter of 2008, although she still has significantly more cash on hand.

The National Republican Senatorial Committee (NRSC) smells a rare pickup opportunity and is trying to paint Landrieu as far to the left of the electorate in a state that has seen a decline in traditionally Democratic urban voters since the displacement caused by Katrina.

“She’s got a very liberal record for a state that is running Republican,” said NRSC spokeswoman Rebecca Fisher, citing as an example Landrieu’s opposition to repealing the estate tax.

Senate Republicans, more than a dozen of whom have contributed to Kennedy’s campaign, also are trying to cast Landrieu, an appropriator, as fiscally irresponsible.

“Any Republican is a good candidate to replace Sen. Landrieu,” said Richard M. Burr, R-N.C., who has donated to Kennedy. “I want somebody that’s consistently trying to reform the federal government and control spending.”

Landrieu’s Democratic allies say her efforts on energy and flood insurance, while a burden to them in the short term, are evidence of her success as a senator.

“She’s a Louisianan first and a Democrat second,” said Arkansas Sen. Mark Pryor, a fellow Southern Democrat who, like Landrieu, often strays from the party line. “She’s found a good groove.”

Said Schumer: “She puts her state above party, and I think people respect that.”