John McCain, the senior senator from Arizona and the GOP’s 2008 presidential nominee, knows he has a bull’s-eye on his back.

The tea party is going after Senator McCain in the Republican primary, as he seeks a sixth term in the Senate. If he clears that hurdle, he’ll face a Democratic challenger in the general election next November.

That task – and the GOP’s larger quest to hold onto the Senate – will be all the more difficult if the party’s presidential nominee is weak, McCain says. At a press breakfast Wednesday hosted by the Monitor, McCain didn’t go after Donald Trump explicitly, but he made clear that he thinks a Trump nomination could hurt other Republican candidates.

“Obviously, we all know from history that if you have a weak top of the ticket, that has a significant effect on the states, particularly the swing states,” McCain said. “I hate to refer to Barry Goldwater, who I loved and admired, but the fact is when Barry Goldwater lost, [Republicans] lost big-time.”

Senator Goldwater of Arizona, whose seat McCain holds, was soundly defeated in the 1964 election against President Lyndon Johnson. Goldwater was seen as too conservative for the times, and he faced a sitting president who had taken over just a year earlier for the slain President John F. Kennedy.

Today, Republicans control the Senate by a margin of just four votes, and they are defending far more seats than the Democrats this cycle. One incumbent senator who could be harmed by a weak GOP nominee, McCain says, is his friend Kelly Ayotte (R) of New Hampshire. She’s locked in a tight reelection race against Gov. Maggie Hassan (D).

“By the way, I’m confident that Kelly will win, don’t get me wrong, but I think it’s a bigger lift,” McCain added.

McCain also went after Mr. Trump (again, not by name) for disparaging Hispanics, as the billionaire real estate developer did when he announced his campaign.

“You cannot alienate the Hispanic voter and expect to win a general election,” McCain said. “You can do the math on it.”

In 2012, GOP nominee Mitt Romney won only 27 percent of the Hispanic vote in his loss to President Obama. In 2016, political analysts say, the Republican nominee will need to win at least 40 percent of the Hispanic vote to win the election.

McCain wasn’t all doom and gloom in the breakfast with reporters. When asked to name the top candidates on national security, he started with his close friend Sen. Lindsey Graham (R) of South Carolina, who is mounting a long-shot bid for the presidency. Then he praised several others.

“I do admire [Chris] Christie’s gumption,” McCain said. “I do admire Jeb Bush’s proposals. I think that John Kasich, who I came to the House with back in ’82, has been a very successful governor in a swing state. Marco Rubio I clearly view as a next generation of leaders in the Republican Party, particularly on national security issues.”

Sen. Ted Cruz (R) of Texas, not surprisingly, didn’t make McCain’s list. The two have clashed regularly, including over Senator Cruz’s tactics that led to the government shutdown of 2013, as well as the National Defense Authorization Act, which Cruz opposed. McCain once called Cruz a “wacko bird.”

Still, McCain promised to support the Republican nominee, whoever that is.

McCain also called on Republican candidates to disavow comments by audience members at campaign events that are sexist or racist.

“You have to repudiate that,” he said. “If you allow those things to be said or done, in the case of beating up a protester, and it goes unresponded to, then you’re complicit.”

At a recent Trump rally in Alabama, a Black Lives Matter activist was punched. Trump not only didn’t call for civility, but he also called the protester “so obnoxious and so loud” that “maybe he should have been roughed up.”

During McCain’s 2008 campaign, he pointedly corrected an audience member who referred to Mr. Obama as a Muslim.

“You have to do what’s right, otherwise you lose in the long run. Even if you win, you lose. Speaking as a loser ...,” McCain said Wednesday, eliciting a laugh from the press. “You just must have a level of political discourse, otherwise the consequences are myriad.”