Samak dissolves parliament to call a snap election
But, with his People Power party - a replacement for the disbanded Thai Rak Thai party of ousted leader Thaksin Shinawatra - almost certain to win again and lead the next government, the PAD is unlikely to give up its campaign.
Samak declares a state of emergency to enlist the help of the military in clearing the tens of thousands of protesters
from the seat of government, but it is far from certain that the military would follow orders.
With the second anniversary of the coup against Thaksin looming on September 19, army chief Anupong Paochinda has stressed that another coup would resolve none of Thailand's underlying political problems.
However, if tensions escalate and people get hurt or killed, the army may feel justified in intervening, citing the
need for national reconciliation, and forcing the government from power.
Samak has so far shown considerable restraint and publicly pledged not to resort to violence, but many wonder how long this can last if protests persist that paralyse his government.
Scores of deaths could result if riot police were sent in to storm the protest zone, where middle-aged women sit
side-by-side with youths armed with stakes, golf clubs and iron bars.
Inevitable public revulsion at bloodshed could trigger Samak's downfall.
Samak could step down along with his cabinet, leaving the opposition Democrat party to cobble together a coalition government.
If it fails, elections would ensue.
Nobody knows who is really backing the PAD, but most analysts suspect the group has deep pockets and is well connected.
With Samak on the back foot, it is unlikely to give up now.
Deeply popular and revered by many Thais, King Bhumibol Adulyadej carries huge informal political clout.
In six decades on the throne he has intervened in several disputes, favouring variously elected or military administrations.
Earlier this month the 80-year-old monarch delivered thinly veiled criticism of government economic policy and its conduct in a spat with the Bank of Thailand over how to tackle inflation.
But a spokesman for Samak told Al Jazeera that at a recent meeting with the king, there was no pressure on the prime minister to resign.