With a pawn on the fourth the Rook can defend from its back rank as there are going to be sufficient checking resources from there for example 1. Ka4 Ra8+ 2. Kb5 Rb8+ 3 Ka5 Ra8+ 4 Kb6 Rb8+ etc
1.Rd4
Ke5
2.Kc3
Rh8
3.Rd7
Ke6
draws [3...Rb8
4.Kc4
Ke6
5.Ra7
Kd6
6.b5
Rc8+
7.Kb4
Rc7
8.b6+-
; 3...Rc8+
4.Kb3
Ke6
5.Rd4
Ke5
6.Rc4
Rb8
7.Rc6
Kd5
8.Ra6+-
] *