(CNN) Donald Trump is once again alone at the top of the Republican field, according to the latest CNN/ORC Poll , with 36% of registered Republicans and Republican-leaning independents behind him, while his nearest competitor trails by 20 points.

Three candidates cluster behind Trump in the mid-teens, including Texas Sen. Ted Cruz at 16%, former neurosurgeon Ben Carson at 14% and Florida Sen. Marco Rubio at 12%. All other candidates have the support of less than 5% of GOP voters in the race for the Republican Party's nomination for president.

Carson (down 8 points since October), former Florida Gov. Jeb Bush (down 5 points to 3%) and Kentucky Sen. Rand Paul (down 4 points to 1%) have lost the most ground since the last CNN/ORC poll, conducted in mid-October.

Cruz (up 12 points) and Trump (up 9 points) are the greatest beneficiaries of those declines. Rubio is also up slightly, gaining 4 points -- an increase within the poll's margin of sampling error -- since the last CNN/ORC poll.

Republican voters are most sharply divided by education. Among those GOP voters who hold college degrees, the race is a close contest between the top four contenders, with Cruz slightly in front at 22%, Carson and Rubio tied at 19% and Trump at 18%. Among those without college degrees, Trump holds a runaway lead: 46% support the businessman, compared with 12% for Cruz, 11% for Carson and just 8% for Rubio.

Several other recent polls have shown Trump reclaiming a solid lead atop the GOP field after several weeks of near parity with Carson. But the new poll finds the businessman with both his broadest support and his widest lead in any national live-interviewer telephone poll since he announced his candidacy in June.

The poll reflects Trump's dominance over the rest of the field on the issues voters deem most important to them. He holds massive margins over other Republicans as the candidate most trusted to handle the economy (at 55%, Trump stands 46 percentage points over his nearest competitor), the federal budget (51%, up 41 points), illegal immigration (48%, up 34 points), ISIS (46%, up 31 points) and foreign policy (30%, up 13 points).

Looking at those Republicans who consider each issue to be "extremely important" to their vote, Trump's standing on each issue is even stronger. Among those Republican voters who call the economy extremely important, for example, 60% say they trust Trump to handle that issue. Among immigration voters, 55% trust Trump on the issue. On foreign policy, Trump inches up to 32%, and among those who call terrorism an extremely important issue, 49% say they trust Trump most on ISIS.

The poll was conducted before the shootings in San Bernardino, California, on Wednesday, carried out by a man reported to have been radicalized and his wife.

More generally, about 4 in 10 Republicans say Trump is the candidate who would be most effective at solving the country's problems (42% name Trump, 14% Carson, 12% Cruz, 10% Rubio) and could best handle the responsibilities of being commander-in-chief (37% Trump, 16% Cruz, 11% Carson and 10% Rubio).

And a majority of Republican voters say they see Trump as the candidate with the best chances to win the general election next November (52% say Trump has the best chances there, compared with 15% for Rubio, 11% for Cruz and 10% for Carson).

On immigration, an issue that has been a focal point of Trump's campaign, most Americans say the government should not attempt to deport all people living in the country illegally (63%), and even more say such a mass deportation wouldn't be possible (81%). About half say such an effort would be harmful to the economy (47%), while about 3 in 10 say it would help (29%).

Among Republicans, a narrow majority (53%) think the government should try to deport all of the estimated 11 million immigrants currently living in the U.S. illegally, but most think it wouldn't ultimately be possible to achieve (73%). Republicans are more likely than others to see a deportation effort as helpful to the economy (44% think it would help, 30% that it would hurt).

There's a sharp divide among Republican voters on these questions about deportation between those who back Trump and those who do not. Among Trump supporters, 67% say the government should attempt to deport all people living in the country illegally, while just 39% of Republican voters backing other candidates agree. Still, even among Trump's supporters, most say it wouldn't be possible to deport all those living in the U.S. illegally (55%).

Republican voters remain more enthusiastic about voting than their Democratic counterparts, but the gains in enthusiasm that had emerged through October appear to have stalled.

The CNN/ORC Poll was conducted by telephone November 27 through December 1 among a random national sample of 1,020 adults. Interviews were conducted with 930 registered voters, including 445 who are Republicans or independents who lean toward the Republican Party. For results among Republican and Republican-leaning voters, the margin of sampling error is plus or minus 4.5 percentage points.