Break with Bush
Obama's first few months have been marked by a firm break with the administration of his predecessor, George Bush, on issues ranging from war and recession to healthcare and climate change.
He has signed a law to close the US prison facility at Guantanamo Bay in Cuba, banned the use of torture on so-called terror suspects, steered a $787bn economic stimulus package through congress and pledged to withdraw most US troops from Iraq by August 2010.
On the economy, Obama listed the steps his administration had taken over the past 100 days, pointing to the passing of the revised draft budget by congress, the expansion of healthcare and tax cuts for working class families and a housing plan to aid homeowners.
But he said his administration still had to "clear away the wreckage" of the US recession and warned that with millions of Americans still without jobs the US "cannot go back to an economy that is built on a pile of sand".
His comments came the same day that the US commerce department said the country's economy shrunk by 6.1 per cent in the first quarter of 2009 amid cuts by businesses and a drop in exports.
While the majority of the new conference focused on domestic issues, on foreign policy, Obama briefly acknowledged that the US still faced threats ranging from "terrorism" to nuclear proliferation to pandemic flu.
|Obama said recent bomb attacks in Iraq
were a cause for concern [AFP]
When asked about waterboarding, Obama reiterated his belief that the controversial "harsh interrogation technique" was torture.
"I think that whatever legal rationales were used, it was a mistake," he said, adding that the US would be stronger by upholding its ideals.
Al Jazeera's Rob Reynolds in Washington says Obama's answers on torture left little doubt as to his personal position on the issue of torture.
However, the US president had also made it clear he considers it up to the justice department to decide on any prosecutions of those who drafted the legal opinions authorising torture.
Obama has tamped down any ideas of such prosecutions, although he has said he could be open to a bipartisan congressional investigation.
Obama also said that the recent "spectacular" bombings in Iraq were a cause for concern but said civilian deaths were lower than in the past, adding that the US was still pressuring the Iraqi government to make progress.
On the swine flu crisis, Obama said the US continued to "closely monitor" the situation and reassured US citizens the government was taking all steps necessary.
The tradition of marking the first 100 days of US presidencies dates back to Franklin D Roosevelt in the 1930s, who used the first 100 days of his presidency to put in place the main components of his programmes aimed at pulling the US out of the Great Depression.