Republican presidential candidate Donald Trump speaks during a town hall campaign event on Monday in Columbus, Ohio. (Evan Vucci/AP)

The last couple of weeks have been nothing short of disastrous for the Republican Party.

No, Donald Trump’s position in the race hasn’t worsened dramatically, nor did the Democratic convention wash away Hillary Clinton’s many political warts. When it comes to the presidential race, we will see what the post-convention polls show.

[In first major poll post-convention, Trump loses bump]

Things have deteriorated for the GOP because Donald Trump’s comments about Russia and Vladimir Putin have further shredded the Republican Party’s historically greatest strength: national security and defense themes.

[How entangled with Russia is Trump?]

Add to that Trump’s — and GOP delegates’ — performance at their convention (“Lock her up!”) and Trump’s positions on trade, taxes, spending and entitlements, which also contradict the long-standing Republican message, and the party is nothing short of a mess.

For many lifelong Republicans and committed conservatives, as well as dozens of down-ballot Republican candidates, the redefinition of their party and the tone of the nominee are simply unacceptable. That’s clearly why Mitt Romney, the Bush family, Sen. Ben Sasse of Nebraska, Sen. Ted Cruz of Texas, Ohio Gov. John Kasich and others refuse to back Trump.

Of course, some high-profile Republicans — from House speaker Paul D. Ryan (Wisc.) to Senate Majority Leader Mitch McConnell (Ky.) and Sen. Marco Rubio of Florida — hesitated to embrace Trump but eventually backed him. They promised (or at least hoped) that Trump would “grow” as a candidate when the general election arrived.

They are still waiting.

After some staff changes, the Trump campaign is quicker to issue clarifications and corrections following the nominee’s interviews. But otherwise Trump has evolved little as a candidate since entering the presidential contest more than a year ago.

Whatever Trump’s personal weaknesses — and the list is very long — he is in the process of undermining the entire rationale for the Republican Party.

Trump’s Republican Party echoes the economic populism of the Democratic Party. It ignores the party’s traditional cultural values, and it now has turned its back on the GOP’s foreign policy worldview. Indeed, Trump’s view of Putin and how countries should “get along” shows the kind of naivete normally associated with the most liberal of Democrats.

Even worse, Trump’s message is not about the limits of political power — it is about the unlimited nature of his own power and abilities.

All of this raises the question of whether Republican officeholders and party leaders who announced their support for Trump will now reverse themselves and pull their endorsements. Though Sen. John McCain of Arizona has come close, it’s very difficult to believe many will take that dramatic step.

Like Ryan and McConnell, most will criticize a Trump statement or otherwise indicate a different point of view. But pulling an endorsement is a much bigger step.

Most, if not all, of those unshakably loyal Republicans apparently have concluded that Clinton is so untrustworthy and her politics so far left that any Republican is preferable, no matter how flawed that person may be. For many, the election is about only the Supreme Court.

It’s easy for those Republicans to rationalize supporting Trump, no matter how vulgar he is or how far his views stray from what only a couple of years ago was Republican orthodoxy. “He’s not Hillary Clinton” covers a lot of Trump’s shortcomings.

Why am I so skeptical that mainstream Republicans who have already climbed out on the Trump limb will turn around and crawl back? Because that is not how American politics works.

Something very similar happened back in 1998, when Democrats circled the wagons and stuck by Bill Clinton even though he had a very inappropriate relationship (including in the Oval Office) with an intern and lied to the American public. Democrats turned the scandal into a partisan fight.

As I wrote in an Oct. 1, 1998, Roll Call column titled “Where’s the Outrage?” “I continue to be surprised, and greatly disappointed, that not a single member of his Cabinet, his senior White House staff or his political team has resigned to protest the President’s behavior and lie.”

“The lack of resignations suggests that members of the administration are either so obsessed with power or so jaded and unprincipled that they can ignore the President’s lies to them and to the country,” I continued.

Like Bill Clinton back then, Trump’s behavior has been so far over the line — with his comments ranging from incoherent to inaccurate to outrageous — that it is remarkable so many Republicans continue to support and defend him.

Can you imagine what Republican officeholders, activists and voters would say if a Democratic presidential nominee acted as Trump has or benefited from Kremlin hacking? (I am sure Democrats would be defending that nominee.)

In spite of all of the talk about weaker parties and the growing number of independents, partisanship runs very deep in American politics. It is easier and probably safer politically to hunker down with fellow partisans than to break from the crowd.

Character and principle are qualities that are in short supply on both sides of the aisle.

But that certainly is nothing new.

Stuart Rothenberg writes about the politics of the presidential and congressional races.