Rubio, in an op-ed published Friday, said that "cordial" dialog would no longer work and Walker, in excerpts released from his speech, said that the world is using the strength of the American response to ISIS to gauge its seriousness about Russia and China.
The two one-time top tier candidates, who both maintain strong support among top fundraisers and party leaders, laid out their hawkish proposals just miles away from each other in the early primary state and minutes apart on Friday.
Rubio largely followed his previously released talking points on China, but also went hard after other world leaders.
He called Russian President Vladimir Putin a "gangster," North Korean leader Kim Jong Un a "lunatic," and Iran Ayatollah Ali Khamenei a "radical, Shi'a cleric."
"If you're a political adversary of Vladimir Putin, you wind up with Plutonium in your drink or shot in the street," Rubio said in response to a question about the top threats to the U.S.
And he predicted the Iran nuclear deal negotiated by President Barack Obama will deliver nuclear weapons to the country.
"A radical, Shi'a cleric is going to develop a nuclear weapon, and he will also have a long-range missile that can hit the United States," Rubio said.
Previewing his China speech in an opinion piece in The Wall Street Journal
, Rubio argued that the United States has chosen to "appease" a China that is as much foe as friend. He also called on President Barack Obama to "downgrade" the upcoming state dinner for Chinese president Xi Jinping to a "working visit."
"This is an opportunity to speak bluntly to this authoritarian ruler and achieve meaningful progress, not to treat him to a state dinner," Rubio writes in the column -- a line he also repeated in his speech on Friday.
Rubio's stance is not quite as sharp as Walker, who flatly called on Obama to cancel the state dinner earlier this week. The Walker campaign blasted out a note late Thursday taking credit for being the first to seek the cancellation of the dinner.
"There's serious work to be done rather than pomp and circumstance. We need to see some backbone from President Obama on U.S.-China relations," Walker said in a statement earlier this week.
Walker's statement was initially panned by pundits as trying to "out-Trump Trump," but conservatives, including radio host Hugh Hewitt, later praised the stance.
But both candidates follow in the steps of Trump, who burst onto the field more than two months ago, with blunt comments about both China and U.S. politicians.
"Our country is in serious trouble. We don't have victories anymore," Trump said in his June 16 announcement. "We used to have victories, but we don't have them. When was the last time anybody saw us beating, let's say, China in a trade deal? They kill us. I beat China all the time. All the time."
Walker recently added tough talk on China to his stump speech, but spent most of the his 25-minute talk to cadets at The Citadel, promising to increase defense spending as a means to stop radical Islam -- including ISIS and Iran.
"Let me be clear: defeating ISIS and rolling back Iran will require a greater investment of U.S. resources. Sternly-worded tweets and isolated air strikes will not destroy this enemy," Walker said.
Walker, who had trained his sights on Washington Republicans last week as he talked up his health care proposal, refocused on Obama and Clinton Friday.
"We continue to deal with these and other disastrous consequences of her decisions as Secretary of State," Walker said. "Everywhere in the world Hillary Clinton has touched is more messed up now than before she and the President took office."