Laura Bush, married to the last Republican president before Trump, took the highly unusual step of publishing a Father's Day op-ed in the Washington Post on Sunday, in which she said "this zero-tolerance policy is cruel".
German Chancellor Angela Merkel has been been given a two-week deadline by her ultra-conservative coalition partner on Monday to adopt stricter migration and asylum rules in agreement with other European Union member states.
Seehofer leads the Bavaria-only Christian Social Union party, the sister party to Merkel's conservative Christian Democratic Union.
Instead, she wants to find a common European solution at the June 28-29 EU summit.
If Merkel is given a two-week ultimatum, she would still have the Herculean challenge of persuading European Union governments to sign up to a common plan on the migrants.
German leader Angela Merkel is facing pushback from her political allies on her open door policy for refugees.
"It's in Germany's interest to achieve a controlled migration in good partnership with our European neighbors", she said. "Others [sic] countries are even worse".
That hope, however, is running up against an "axis of the willing" to combat immigration announced last week by Italy's new far-right interior minister and his German and Austrian counterparts.
The inflow of migrants is "a European challenge that requires a European answer". She also called for doing more to stop human smugglers.
The Italian government is proposing so-called "hotspots" in migrants' countries of origin or transit to prescreen asylum candidates before they set out for Europe. France said ahead of the talks that if Merkel and Macron didn't agree on strengthening the eurozone and dealing with migration, the bloc was likely to return to turbulent times.
Seehofer's CSU party is due to meet Monday to decide which course to take. "We will fight for that, and on this point there's no latitude for the chancellor." he added. "But we stand by our position that, if this does not succeed, turning people back immediately at the border must be possible".
National contributions and European resources would be used to fund the budget, the leaders said in the declaration.
The spat over immigration has laid bare the deep tensions in a fractious German government that took office only in March, after almost six months of postelection haggling. A regional party in her ruling coalition is demanding tighter rules for migrants entering the country, and that party vows to act unilaterally if the chancellor refuses.
Both Macron and Merkel highlighted the need for the EU's external borders to be strengthened by boosting the so-called Frontex border and coast-guard agency.
If Seehofer were to defy her and go ahead with his plans on Monday, Merkel would nearly certainly be forced to fire him.
At the centre of the tensions there is Mrs Merkel's widely criticised immigration programme, which brought more than a million refugees in the country in 2015.