Republican presidential candidate Donald Trump is surging not only in national polls but also in key early-state polls.

In a latest CNN/ORC survey, he leads the Republican race with a support of 18%. That's up 6 points from a poll in late June.

Trailing behind Trumo is former Florida governor Jeb Bush with a support of 15%, with Wisconsin Governor Scott Walker getting 10%. Those numbers for Bush and Walker were almost the same as in the June poll.

None of the other 14 contenders received double-digit support.

A majority of Republicans say it is still too early to say whom they are going to vote for. But they want Trump to stay in the race, despite his controversial comment saying Senator John McCain is no war hero.

The CNN/ORC poll was conducted in July 22-25, with a margin of error of plus or minus 3.5 percentage points among registered voters who were part of the survey.

In an NBC/Marist poll, Trump is also leading with a 21% support from potential Republican primary voters in New Hampshire. That's a significant lead over Bush who only had 14%. Walker is third with 12%.

In Iowa, Trump, with a support of 17%, is 2 points behind Walker. Bush is third with 12%. The poll shows an improvement in Trump's position in Iowa after his remarks against McCain, although not the same could be said in New Hampshire.

In hypothetical matchups, the real estate magnate trails Democratic rivals Hillary Clinton and Senator Bernie Sanders by wide margins.

According to CNN, Clinton leads all presidential candidates, followed by Bush and Walker who are about even with Sanders.

Among Democrats, Clinton has support of 56%, Sanders 19% (up from 15% in June), according to the CNN/ORC poll.

But Clinton's image is negative. Among registered voters, 44% have a positive impression of her, while 49% have an unfavorable view.

Still, that is so much better than Trump's. The developer is least-liked among all candidates, with 59% of all registered voters having an unfavorable impression of him, according to CNN.

Trump faces off with other Republican contenders in their first debate on August 6.