Donald Trump jumps to an 18-point lead over Ted Cruz this week with record high support for the Republican nomination.

Trump tops Cruz by 45-27 percent among GOP primary voters in a new Fox News national poll on the 2016 election. John Kasich comes in third with 25 percent.

Three weeks ago, the mogul was up by three over Cruz: 41-38 percent, with Kasich at 17 percent (March 20-22, 2016).

Forty-five percent is a new high for Trump. The previous high was last month’s 41 percent.

CLICK TO READ THE POLL RESULTS

Trump’s best numbers come from GOP voters without a college degree (54 percent) and those who describe themselves as “very” conservative (50 percent).

In contrast, the Democratic race tightened. Clinton is ahead by two points, edging Bernie Sanders by 48-46 percent. Last month, before Sanders won eight of the nine most recent contests, she had a 13-point advantage (55-42 percent).

The shift comes from women. Clinton’s support has declined 11 points among women, while support for Sanders is up by nine. Support among men mostly held steady -- and it’s in Sanders’ favor: 57-37 percent.

Kasich does best against Democrats, Trump worst

Kasich, who is in third both in polling and the delegate count, likes to tell folks on the campaign trail that most polls show he’s the only Republican who can win in November.

That holds true in these new potential matchups.

Kasich is up by nine points over Clinton (49 vs. 40 percent), while she’s the one who tops Trump (+7 points) and Cruz (+1 point).

The Ohio governor also does best against Sanders. The Vermont senator trounces Trump (+14 points) and Cruz (+12 points). Against Kasich, he’s up by just four points.

Still, when voters are asked which Republican candidate has the best chance to defeat Clinton, they pick Trump first (42 percent), followed by Cruz (24 percent) and Kasich (20 percent). GOP primary voters are even more bullish on Trump: 58 percent say he has the best odds, while 21 percent say Cruz and 16 percent Kasich.

"When it comes to electability, the disconnect between what Republicans think and what the polling data show is astounding," says Daron Shaw, Republican pollster who conducts the Fox News Poll with Democratic pollster Chris Anderson. "Close to three times as many think Trump has the best chance against the Democrats despite the fact he's down seven points to Clinton while Kasich is up nine."

Pollpourri

Voters see two nomination battles of strikingly different character. Eight in 10 say the Republican campaign is “rude and disrespectful” (80 percent), while most think the Democratic side is “polite and respectful” (64 percent).

The Fox News poll is based on landline and cellphone interviews with 1,021 randomly chosen registered voters nationwide and was conducted under the joint direction of Anderson Robbins Research (D) and Shaw & Company Research (R) from April 11-13, 2016. The poll has a margin of sampling error of plus or minus three percentage points for all registered voters, and 4.5 points for both the Democratic (450) and Republican primary voter samples (419).