By Jim Muir
BBC News, Beirut
The last time a US vice-president came to Beirut was in 1983, when George Bush Senior flew hurriedly in following a suicide truck bomb attack which blew up a US marine barracks, killing more than 240 soldiers.
That, and a similar demolition of the US embassy in Beirut, persuaded President Ronald Reagan to pull the marines out of Lebanon, a humiliating retreat in the face of local forces backed by Syria and Iran.
More than 25 years on, was Vice-President Joseph Biden visiting Lebanon in the hope of averting another big setback to US influence at the same hands - but this time at the polling booths?
After talks with President Michel Suleiman - who is regarded as neutral in the sharply-polarised Lebanese arena - Mr Biden insisted he had not come to back any Lebanese party or person, but rather to support the country's independence and sovereignty.
But at the same time, he urged "those who think about standing with the spoilers of peace not to miss this opportunity to walk away from the spoilers" - a remark clearly aimed at Hezbollah and its allies.
Although the outcome hinges on voting results in a few hard-to-predict constituencies, the Hezbollah-led opposition stands a good chance of coming out narrowly ahead of the Western-backed coalition that the Americans would clearly like to see win.
Posters of Lebanese electoral candidates
Washington will review its relations with Lebanon after the election
Mr Biden also warned of likely consequences if Hezbollah and its allies were to prevail in the 7 June poll and form the kind of government Washington would frown on.
The administration, he said, "will evaluate the shape of our assistance programmes based on the composition of the new government and the policies it advocates."
He then went off to see the Speaker of the Lebanese parliament, Nabih Berri, who is an ally of Hezbollah, and the Prime Minister, Fuad Siniora, who belongs to the Western-backed coalition.
If that implied balance, the impression was swiftly undermined by a later, unpublicised meeting behind closed doors in a private home with leaders of the pro-Western coalition who hold no official posts.
But Mr Biden insisted that Washington's commitment was to Lebanon, its sovereignty and independence.
To back that up, he appeared with the Defence Minister, Elias al-Murr, at a display of some of the military hardware the US has supplied to the Lebanese Army in recent years.
Mr al-Murr said that, in a visit to Washington last month, he had been given a written commitment by Defence Secretary Robert Gates to provide the Lebanese Army with hundreds of millions of dollars' worth of arms and training over a five-year period, including helicopters and drones.
Although that commitment might be reviewed in the light of the election results, Washington seems confident that the Lebanese Army can hold together and be built on as a neutral national institution despite the strain of coexistence with Hezbollah, whose military strength is greater.
Despite Mr Biden's protestations of neutrality, Hezbollah itself lost no time in dubbing his visit "a clear and detailed interference in Lebanese affairs" which raised "strong doubts about its real motivations."
Hezbollah supporters at a rally on 22 May ,2009
Thousands of Hezbollah supporters rallied to hear the party leader's speech
As Mr Biden was showing off US military hardware in Beirut, Hezbollah was staging its own show of strength in Nabatieh, a provincial centre south-east of the capital.
Thousands of supporters gathered to watch a relayed speech from their leader, Sheikh Hassan Nasrallah, to mark the anniversary of Israel's ignominious withdrawal from Lebanon in 2000 under the pressure of Hezbollah attacks.
But US leaders may already have concluded that a narrow win by the Hezbollah-led coalition would not be the end of the world.
Hezbollah itself is only putting forward 11 candidates in the contest for 128 parliamentary seats.
The other elements in the opposition coalition come from allies such as the mainstream Shia Amal movement, headed by parliamentary Speaker Nabih Berri, and the Free Patriotic Movement of the Christian leader Michel Aoun, once a fierce opponent of Syria but now reconciled with Damascus and likely to do well in many Christian areas.
So, while generally unwelcome to the West, a narrow victory by the opposition would produce a picture very different from, for example, the Hamas takeover in Gaza, which was violent and absolute.
The lines could be further blurred if Washington's diplomatic overtures to the Lebanese opposition's backers, Iran and Syria, were to produce results.
The Americans' closest ally, Britain, is already allowing its diplomats to hold official contacts with Hezbollah's "political wing", although the movement is still shunned by Washington as a "terrorist" group.