If other NATO nations they think about it, it's not just Trump.NATO is already making plans for the US to be out and it's directly because of him.
Over 28 years, they will have had 12 years with Obama and Biden and a likely 16 years with Bush II, Trump's terms. Ignoring incumbent victories, the US has chosen a disaster for a new leader 3 out of 5 times. That mix suggests an underlying fickleness in the manner in which the US picks its leaders (with both electorate and system factors), and that the US is picking a leader hostile to the reliable, ordered approach they presumably valued in the US as a partner.
If and when the US selects leaders who want to work productively (assuming things are not blown entirely apart), then the order of the day should be nothing more than duct tape and chewing gum for existing agreements and short term transactionalism until the US demonstrates a track record sanity, which would require the selection of responsible leadership over at least two--and probably three or more--decades.