Lower, a pro-Trump Republican, announced Monday he would run against Amash in the Republican primary for Michigan's 3rd Congressional District next year -- after the incumbent on Twitter called President Donald Trump's conduct "impeachable" and sparked an intraparty feud.
"Like a lot of people I was pretty angry by the tweets, but more immediately -- right after that -- I decided that the campaign that we'd been planning to announce in July, it would be a good idea to move that up in terms of the announcement and that's what we've done," he said on Michigan's Big Show, a Michigan radio show. "Today, we're announcing that I'm going to challenge Congressman Amash in the Republican primary this fall -- or next fall, rather."
"I want to work with the president, I want to work with other Republicans both in the House and Senate and actually get things done for our state and for our country," he continued.
Lower moved up his timeline for announcing his candidacy for the U.S. House after Amash tweeted Saturday that he believes Trump "engaged in impeachable conduct" after reading special counsel Robert Mueller's redacted report about the investigation into the 2016 presidential election.
Here are my principal conclusions:— Justin Amash (@justinamash) May 18, 2019
1. Attorney General Barr has deliberately misrepresented Mueller's report.
2. President Trump has engaged in impeachable conduct.
3. Partisanship has eroded our system of checks and balances.
4. Few members of Congress have read the report.
He added that he has seen "tremendous amount of encouragement" to run from grassroots groups, voters, donors and other party officials, which he said was a result of Amash "not being effective at all."
Lower asserted that Amash has not been "able to get anything done by isolating and marginalizing himself within the Republican caucus there in D.C. And then when you add the basically the ardent opposition to Trump and anything Trump wants to do, it's just sort of the cherry on top of a body of work that shows that he's been completely ineffective as our congressman."
"He's one of only four Republicans to vote against a balanced budget, one of only eight to vote against supplying Israel with aide, voted against cutting funding to Planned Parenthood," he said of Amash's record. "Pretty much the only Republican to vote against a resolution supporting ICE. Only Republican to vote for allowing illegal immigrants to vote in local elections. Bottom line is, he hasn't been effective. At the end of the day, he's got one bill signed into law and 10 years in Congress and it was to rename a post office."
Lower teased his announcement on Saturday, hours after Amash's tweets, writing on Twitter, "This cannot go unchallenged. I support Michigan values, I support Donald J. Trump, I support our party's values and I will have a major announcement regarding Michigan's 3rd Congressional District this week."
Lower's entrance tees up a tough re-election fight for Amash who was first elected to the seat in 2010, when he rode the tea party wave as a conservative star. He hasn't faced a primary challenge since 2014 when he beat Brian Ellis, a businessman from Grand Rapids, Michigan by nearly 15 percentage points.
In the 2016 presidential election, as Michigan tilted in Trump's favor, the first time a Republican won the state since 1988, Trump also carried the 3rd Congressional District handily over Hillary Clinton.
Despite the fallout of his decision to stand at odds with the core of the Republican Party, Amash reinforced his position about why Trump's behavior meets the threshold of impeachment in a new series of tweets Monday, in which he also indirectly addressed the political consequences.
"America's institutions depend on officials to uphold both the rules and spirit of our constitutional system even when to do so is personally inconvenient or yields a politically unfavorable outcome," he wrote.
Later, he flatly dismissed the primary challenge, telling ABC News on Capitol Hill, "It’s not serious ... I feel very confident in my district."
He added that he believes his constituents "are supportive" overall.
America's institutions depend on officials to uphold both the rules and spirit of our constitutional system even when to do so is personally inconvenient or yields a politically unfavorable outcome. Our Constitution is brilliant and awesome; it deserves a government to match it.— Justin Amash (@justinamash) May 18, 2019
Amash did not endorse the president in 2016, but his survival in 2020 is splintering between whether his supporters at home will back him -- despite his opposition to Trump -- or favor another Republican who is eagerly campaigning for Trump's endorsement.
At the same time, speculation about Amash weighing a 2020 Libertarian presidential run against Trump re-emerged as recent as last month, when he told CNN he hasn't ruled it out.
"I'd never rule anything out, that's not on my radar right now, but I think it is important that we have someone in there who is presenting a vision for America that is different from what these two parties are presenting," he said in April.
ABC News' John Parkinson and Will Steakin contributed to this report.