Fully seven weeks before he is due to take office, President-elect Donald Trump launched what looked like an offensive against China starting last week. His apparent strategy of pushback against the regime of Xi Jinping has some merit. What’s worrying is the evident lack of preparation and diplomatic care in the initiative, as well as its possible unintended consequences.

On Friday, in a move that was reportedly planned, Trump took a congratulatory phone call from Taiwanese President Tsai Ing-wen, breaking with decades of U.S. policy. When the United States formally opened diplomatic relations with China in 1979, Taiwan was relegated to nondiplomatic status, which has meant arms sales and support but not phone calls or meetings at the highest level. China views Taiwan as a breakaway province and has always been hypersensitive to any quiver in its standing in the world, and especially its ties to the United States.

The phone call predictably raised alarms in Beijing. It may produce countermoves – such as new economic and military pressures on Taiwan – that may undercut the call’s political boost to Taipei while further stoking already-high tensions in East Asia.

The president-elect did not stop with the phone call. Next came Twitter messages on Sunday that echoed his campaign blasts against China on economic issues and the South China Sea.

If Trump wants to effectively challenge China, a rash of tweets hardly seems the right way to go about it. He has been acting without the benefit of U.S. intelligence briefings or advice from the State Department, and his weekend missives were apparently uncoordinated with the current administration. His impulsive statements carry the risk of misunderstanding and miscalculation.

Riling China also could have a downside when Trump needs to ask Beijing for help with its errant client state, North Korea. This is just one example of the costs and benefits Trump should weigh – preferably with experienced advisers – before letting fly on Twitter.