Hillary Clinton formally clinched the Democratic Party's presidential nomination Tuesday as opinion polls point to increasingly ominous signs against her bid to become the first female president in U.S. history.

The former secretary of state and first lady received a majority of delegates in a state-by-state roll call vote on the second day of a four-day national convention held at Wells Fargo Center in Philadelphia.

She is the first female presidential nominee of a major party in U.S. history.

Clinton is scheduled to deliver a speech accepting the nomination on Thursday, the final day of the convention. She is expected to use the speech not only to make the case for her bid but to highlight how unfit her Republican rival Donald Trump is for the White House.

Her nomination came as signs of negative voter sentiment about her are growing.

According to U.S. media, the latest Gallup poll showed that Clinton's unfavorable rating reached an all-time worst in her political career.

The survey showed that only 38 percent of the respondents view Clinton favorably, compared with 55 percent in 2014. Moreover, the rating marked a 3 percentage point fall in just one month, down from 41 percent favorable last month, according to the report.

Clinton's favorable rating reached a peak of 67 percent in late 1998.

Her image has been dealt a serious blow by the scandal surrounding her use of private servers to deal with state secrets and other classified information. She has also been accused of mishandling the 2012 attack on the U.S. diplomatic post in Benghazi, Libya, that left the then U.S. ambassador there and three other Americans killed.

On Monday, a series of voter surveys put her behind Trump.

A CNN poll of 1,001 people showed Trump had 48 percent of support, 3 percentage points more than Clinton. A Los Angeles Times survey also put Trump's rating at 45 percent against Clinton's 41 percent. A Gravis poll showed a similar result.

Clinton's foreign policy is not expected to differ much from that of President Barack Obama.

She advocates stronger relations with South Korea and other allies, saying in a major foreign policy speech last month that the U.S. is stronger and safer thanks to the "power of allies." She also said that alliances are a "source of strength."

Referring to Trump's call for allies to pay up for American defense support, Clinton said that allies should pay their fair shares, and many of them have already increased their spending.

On North Korea, Clinton is also expected to continue the current administration's policy of pressuring Pyongyang.

Jake Sullivan, head of the Clinton campaign's foreign policy team, said earlier this year that sharply increasing pressure on the North would be the only way to get the communist regime to participate in authentic negotiations over its nuclear program. (Yonhap)