The 81-year-old Democrat will hope the strikes on Huthi rebels project an image of strength at home and abroad, countering criticism of his leadership by Republicans led by Donald Trump.

But the risk of further inflaming the Middle East after the October 7 Hamas attacks on Israel will weigh heavily on a president who had vowed to extract America from its "forever wars" in the region.

The immediate tone from Biden was tough, saying Washington and its allies had sent a "clear message" that they "will not tolerate" further attacks on shipping in the Red Sea, one of the world's most important sea lanes.

"We will make sure we respond to the Huthis if they continue this outrageous behavior," Biden told reporters on an election campaign trip in the battleground state of Pennsylvania.

"I don't think the strikes will politically help or hurt Joe Biden as long as they remain limited," Garret Martin, who teaches at American University in Washington, told AFP.

"Joe Biden does not want to be dragged into another conflict in the Middle East and that was the same for many of his predecessors. But if he doesn't do anything, the credibility of the US will be viewed as being challenged."

- 'Dropping bombs' -

Republicans have however repeatedly called into question Biden's personal credibility on the international stage as campaigning escalates for one of the most polarizing elections in memory.

Despite the foreign policy chaos of his own time as president, Trump used the Yemen strikes to remind voters of the disastrous 2021 US military withdrawal from Afghanistan on the watch of his likely rival in November.

Trump -- who launched air strikes on Syria in 2018 and was at the helm of the US-led coalition against the Islamic State jihadist group -- attacked Biden for "dropping bombs all over the Middle East, AGAIN."

The Yemen strikes also came a day after Trump's rivals for the Republican nomination, Nikki Haley and Ron DeSantis, had called Biden weak on foreign policy during a debate.

Haley said Biden was "slow" in taking on Iran and the Huthis, and of "hiding in a corner," while DeSantis accused Biden of "kneecapping" Israel's military campaign against Hamas.

Republicans have also zeroed in on Biden's age -- he is America's oldest ever president -- to suggest that he's unfit to be commander in chief.

A further factor in the mix is the row over US Defense Secretary Lloyd Austin keeping his hospitalization for cancer treatment secret from Biden for days as the crisis in the Red Sea mounted.

The White House said Austin was fully involved in the planning for the attack, but that has not stopped critics from suggesting Biden has lost his grip on his own cabinet.

- 'Nervous' -

Driven by animosity towards Iran, many Republicans have backed the strikes on Yemen but, like US House of Representatives Speaker Mike Johnson, suggested they were "long overdue."

"America must always project strength, especially in these dangerous times," Johnson tweeted.

Biden faces opposition too from the left-wing of his own Democratic Party, which also opposes his support for Israel's Gaza offensive.

Rashida Tlaib, the only Palestinian American in Congress, accused Biden of violating the US Constitution by carrying out air strikes in Yemen without congressional approval.

"The American people are tired of endless war," she added.

Biden was quick to stress on Friday that he didn't think there were any civilian casualties from the strikes.

Ultimately Biden's calculus may have depended on two issues that tend to concern US voters -- boots on the ground, and money.

With US troops in Syria and Iraq repeatedly coming under attack from Iranian proxies, failure to act against the Huthis could have sent a bad sign.

But a bigger issue may have been the Red Sea's status as a global economic chokepoint.

Continued Huthi attacks could cause prices of food and gasoline to spike for US consumers at the worst possible time for Biden's reelection hopes.

"It's an election year, it's no surprise that the Biden administration is particularly nervous about this subject," said Martin.