Hillary Clinton has rapidly expanded her lead over Donald Trump since the two presidential hopefuls were running neck-and-neck last month, holding a 12-point advantage over her Republican opponent in a new Monmouth University national poll.

Clinton leads Trump 46 to 34 percent in the latest survey of registered voters, marking a 10-point increase in support for the former secretary of state from a poll taken before both parties' national conventions. Among likely voters, Clinton's lead over Trump expands to 13 points – 50 to 37 percent.

Much of Clinton's post-convention surge appears to stem from her improved standing among members of her own party. More than 9 in 10 Democratic respondents in the poll released Monday said they are committed to supporting the former first lady in November, while 79 percent of Republicans were firmly behind Trump.

Trump maintains a slight edge over Clinton among independent voters — 32 to 30 percent — but his support has decreased drastically since before the GOP held its convention last month. The candidate has spent the weeks since both conventions embroiled in controversy after he confronted the father of a fallen Muslim-American Army captain who spoke out against him at the Democratic convention in late July. Libertarian presidential nominee Gary Johnson has grown his support among independents by 7 points since last month.

As Trump's campaign struggles to get itself back on track and convince the candidate to stay on message, fewer voters believe he is "temperamentally fit" to be the next commander in chief. The percentage of Americans who view Trump as fit to serve has dropped 5 points since July, while Clinton has seen a net gain of 9 points in this category.

Other interesting findings:

  • While electoral enthusiasm among Republicans and independents has plummeted since last June, Democrats remain optimistic about the state of the race.

  • Poll respondents were more familiar with Trump's running mate, Indiana Gov. Mike Pence, than Clinton's, Virginia Sen. Tim Kaine.

  • Trump's current lead among white voters (43 to 38 percent) is 15 points smaller than the lead Mitt Romney carried over President Obama in 2012.

The Monmouth University poll of 803 registered voters was conducted from Aug. 4-7. Results contain a margin of error plus or minus 3.5 percentage points.