David Jackson

USA TODAY

Once again, the more disciplined Donald Trump is giving way to the Twitter-wielding Donald Trump.

After a stretch of more low-key campaigning, Trump is spending the weekend under fire for comments about Hillary Clinton that seem to invite violence against her, fighting with the media, and engaged in a dispute with a former Republican defense secretary — all on top of a revival of the "birther" issue involving President Obama.

The Republican presidential nominee is also virtually tied with Clinton in recent election polls, and says voters are responding to his message about striking back at economic decline, foreign policy turmoil and specific issues like illegal immigration.

"A lot of people agree with me" on immigration, Trump said during a speech Saturday in Houston. "It seems everybody agrees. ... You almost say, what's not to agree with?"

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Eric Schiffer, an independent political consultant, said Trump seems to revert to more aggressive form whenever he is doing well and his polls are up: "Something happens, and he seems to lose the discipline that has helped him."

Trump engaged in more traditional campaigning Saturday, devoted in part to immigration. Speaking in Houston to The Remembrance Project, a non-profit that according to its website "advocates for families whose loved ones were killed by illegal aliens," Trump said that "not one more American life should be given up in the name of open borders."

The Houston trip came a day after Trump sought to put the birther issue behind him, reading a brief statement saying he finally believes Obama "was born in the United States, period." After more that five years of claims that Obama may have been born in another country, Trump did not explain his change of position.

Hours later on Friday, Trump again raised the specter of violence against Clinton. Claiming that his Democratic opponent opposes gun ownership rights, Trump suggested that her "bodyguards" drop their weapons and disarm: "Take their guns away, she doesn't want guns — take them, let's see what happens to her."

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Clinton campaign manager Robby Mook called the comment "out of bounds," and said "we've seen again and again that no amount of failed resets can change who Donald Trump is."

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The Clinton campaign and allies said this isn't the first time Trump has linked potential violence to the Democratic nominee. Last month, while discussing Clinton, gun rights and the Supreme Court, Trump said: "If she gets to pick her judges, nothing you can do folks. ... Although the Second Amendment people, maybe there is, I don’t know."

Taking on Twitter early Saturday, Trump explained his latest comment in terms of the right to bear arms: "Crooked Hillary wants to take your 2nd Amendment rights away. Will guns be taken from her heavily armed Secret Service detail? Maybe not!"

Trump continued to stay busy on Twitter Saturday, striking back at former Defense Secretary Robert Gates for pointed criticism.

Gates, appointed to the Pentagon by President George W. Bush and retained by Obama, criticized both Trump and Clinton in a Wall Street Journal op-ed on challenges facing the next commander-in-chief. But while Clinton has "credibility issues," Gates wrote that Trump is in a "league of his own" and is unqualified for the job.

Donald Trump returns fire from former defense secretary Robert Gates

“He has no clue about the difference between negotiating a business deal and negotiating with sovereign nations,” Gates wrote. “A thin-skinned, temperamental, shoot-from-the-hip and lip, uninformed commander-in-chief is too great a risk for America.”

Trump counter-attacked by tweeting that "I never met former Defense Secretary Robert Gates. He knows nothing about me. But look at the results under his guidance — a total disaster!"

The Republican nominee also expressed displeasure with the media in a string of Saturday tweets.

For example: "@CNN just doesn't get it, and that's why their ratings are so low — and getting worse. Boring anti-Trump panelists, mostly losers in life!"

For another: "Crazy Maureen Dowd, the wacky columnist for the failing @nytimes, pretends she knows me well--wrong!"

In recent weeks, the lower-key Trump has engaged in outreach to African-American voters and to women voters, two groups that give him low ratings in part because of involvement with "birther" attacks on Obama.

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While Trump and aides may be seeking to bury the issue, it is likely to surface during the series of three debates with Clinton that start on Sept. 26.

Clinton "should be able to score points on this with suburban women who will decide this election," said Schiffer, the political strategist and chairman of ReputationManagementConsultants.com.

Less than two months before the Nov. 8 election, some analysts see two Trumps: one who appeals to nationalist conservatives, another seeking to reach more moderate Republican suburbanites, particularly women. Nicole Hemmer, an assistant professor at the University of Virginia's Miller Center, said it seems like he's "telling people what they want to hear."

Hemmer added: "I would guess we're going to see these two Trumps throughout the rest of the campaign."